第十一章 字符串和字符串函数
程序清单11.1，strings1.c:
// strings1.c
#include
#define MSG "I am a symbolic string constant."
#define MAXLENGTH 81
int main(void)
{
char words[MAXLENGTH] = "I am a string in an array.";
const char * pt1 = "Something is pointing at me.";
puts("Here are some strings:");
puts(MSG);
puts(words);
puts(pt1);
words[8] = 'p';
puts(words);
return 0;
} 输出结果：
程序清单11.2，strptr.c:
/* strptr.c -- 把字符串看作指针 */
#include
int main(void)
{
printf("%s, %p, %c\n", "We", "are", *"space farers");
return 0;
} 输出结果：
程序清单11.3，addresses.c:
#include
#define MSG "I'm special"
int main(void)
{
char ar[] = MSG;
const char * pt = MSG;
printf("address of \"I'm special\": %p \n", "I'm special");
printf("address of ar: %p\n", ar);
printf("address of pt: %p\n", pt);
printf("address of MSG: %p\n", MSG);
printf("address of \"I'm special\": %p \n", "I'm special");
return 0;
} 输出结果：
程序清单11.4，arrchar.c:
#include
#define SLEN 40
#define LIM 5
int main(void)
{
const char * mytalents[LIM] = { // 指针的数组
"Adding numbers swiftly",
"Multyplying accurately", "Stashing data",
"Following instructions to the letter",
"Understanding the C language"
};
char yourtalents[LIM][SLEN] = {
"walking in a straight line",
"Sleeping", "Watching television",
"Mailing letters", "Reading email"
};
int i;
puts("Let's compare talents.");
printf("%-36s %-25s\n", "My Talents", "Your Talents");
for (i = 0; i < LIM; i++)
printf("%-36s %-25s\n", mytalents[i], yourtalents[i]);
printf("\nsizeof mytalents: %zd, sizeof yourtalents: %zd\n",
sizeof(mytalents), sizeof(yourtalents));
return 0;
} 输出结果：
程序清单11.5，p_and_s.c:
/* p_and_s.c -- 指针和字符串 */
#include
int main(void)
{
const char * mesg = "Dont't be a fool!";
const char * copy;
copy = mesg;
printf("%s\n", copy);
printf("mesg = %s; &mesg = %p; value = %p\n", mesg, &mesg, mesg);
printf("copy = %s; © = %p; value = %p\n", copy, ©, copy);
return 0;
} 输出结果：
程序清单11.6，getsputs.c:
/* getsputs.c -- 使用 gets() 和 puts() */
#include
#define STLEN 81
int main(void)
{
char words[STLEN];
puts("Enter a string, please.");
gets(words); // 典型用法
printf("Your string twice:\n");
printf("%s\n", words);
puts(words);
puts("Done.");
return 0;
} 输出结果：
程序清单11.7，fgets1.c:
/* fgets1.c -- 使用 fgets() 和 fputs() */
#include
#define STLEN 14
int main(void)
{
char words[STLEN];
puts("Enter a string, please.");
fgets(words, STLEN, stdin);
printf("Your string twice (puts(), then fputs()):\n");
puts(words);
fputs(words, stdout);
puts("Enter another string, please.");
fgets(words, STLEN, stdin);
printf("Your string twice (puts(), then fputs()):\n");
puts(words);
fputs(words, stdout);
puts("Done.");
return 0;
} 输出结果：
程序清单11.8，fgets2.c:
/* fgets2.c -- 使用 fgets() 和 fputs() */
#include
#define STLEN 10
int main(void)
{
char words[STLEN];
puts("Enter string (empty line to quit):");
while (fgets(words, STLEN, stdin) != NULL && words[0] != '\n')
fputs(words, stdout);
puts("Done.");
return 0;
} 输出结果：
程序清单11.9，fgets3.c:
输出结果：
/* fgets3.c -- 使用 fgets() */
#include
#define STLEN 10
int main(void)
{
char words[STLEN];
int i;
puts("Enter strings (empty line to quit):");
while (fgets(words, STLEN, stdin) != NULL && words[0] != '\n')
{
i = 0;
while (words[i] != '\n' &&words[i] != '\0')
i++;
if (words[i] == '\n')
words[i] = '\0';
else // 如果 word[i] == '\0'，则执行这部分代码
while (getchar() != '\n')
continue;
puts(words);
}
puts("Done");
return 0;
} 
程序清单11.10，s_gets.c:
char * s_gets(char * st, int n) // fgets() 函数可能读入换行符
{
char * ret_val;
int i;
ret_val = fgets(st, n, stdin);
if (ret_val) // 即，ret_val != NULL
{
while (st[i] != '\n' && st[i] != '\0')
i++;
if (st[i] == '\n')
st[i] = '\0';
else
while (getchar() != '\n')
continue;
}
return ret_val;
}程序清单11.11，scan_str.c:
/* scan_str.c -- 使用 scanf() */
#include
int main(void)
{
char name1[11], name2[11];
int count;
printf("Please enter 2 names.\n");
count = scanf("%5s %10s", name1, name2);
printf("I read the %d names %s and %s.\n", count, name1, name2);
return 0;
} 输出结果：
程序清单11.12，put_out.c:
/* put_out.c -- 使用 puts() */
#include
#define DEF "I am a #defined string."
int main(void)
{
char str1[80] = "An array was initialized to me.";
const char * str2 = "A pointer was initialized to me.";
puts("I'm an argument to puts().");
puts(DEF);
puts(str1);
puts(str2);
puts(&str1[5]);
puts(str2 + 4);
return 0;
} 输出结果：
程序清单11.13，put1.c:
/* nono.c -- 千万不要模仿! */
#include
int main(void)
{
char side_a[] = "Side A";
char dont[] = { 'W', 'O', 'W', '!' };
char side_b[] = "Side B";
puts(dont); /* dont 不是一个字符串 */
return 0;
} 输出结果：
程序清单11.14，put1.c:
/* put1.c -- 打印字符串，不添加 \n */
#include
void put1(const char * string) /* 不会改变字符串 */
{
while (*string != '\0')
putchar(*string++);
} 程序清单11.15，put2.c:
/* put2.c -- 打印一个字符串，并统计打印的字符数 */
#include
int put2(const char * string);
int main(void)
{
int num;
num = put2("pizza");
printf("%d\n", num);
return 0;
}
int put2(const char * string)
{
int count = 0;
while (*string)
{
putchar(*string++);
count++;
}
putchar('\n');
return count;
} 输出结果：
程序清单11.16，put_put.c:
/* Put_put.c -- 用户自定义输出函数 */
#include
void put1(const char *);
int put2(const char *);
int main(void)
{
put1("If I'd as much money");
put1(" as I could spend,\n");
printf("I count %d characters.\n",
put2("I never would cry old chairs to mend."));
return 0;
}
void put1(const char * string)
{
while (*string) /* 与 *string != '\0' 相同 */
putchar(*string++);
}
int put2(const char * string)
{
int count = 0;
while (*string)
{
putchar(*string++);
count++;
}
putchar('\n');
return(count);
} 输出结果：
程序清单11.17，test_fit.c:
/* test_fit.c -- 使用缩短字符串长度的函数 */
#include
#include /* 内含字符串函数原型 */
void fit(char *, unsigned int);
int main(void)
{
char mesg[] = "Things should be as simple as possible,"
" but not simpler.";
puts(mesg);
fit(mesg, 38);
puts(mesg);
puts("Let's look at some more of the string.");
puts(mesg + 39);
return 0;
}
void fit(char * string, unsigned int size)
{
if (strlen(string) > size)
string[size] = '\0';
} 输出结果：
程序清单11.18，str_cat.c:
/* str_cat.c -- 拼接两个字符串 */
#include
#include /* 提供 strcat() 函数原型 */
#define SIZE 80
char * s_gets(char * st, int n);
int main(void)
{
char flower[SIZE];
char addon[] = "s smell like old shoes.";
puts("What is your favorite flower?");
if (s_gets(flower, SIZE))
{
strcat(flower, addon);
puts(flower);
puts(addon);
}
else
puts("End of file encountered!");
puts("bye");
return 0;
}
char * s_gets(char * st, int n)
{
char * ret_val;
int i = 0;
ret_val = fgets(st, n, stdin);
if(ret_val)
{
while (st[i] != '\n' && st[i] != '\0')
i++;
if (st[i] == '\n')
st[i] = '\0';
else
while (getchar() != '\n')
continue;
}
return ret_val;
} 输出结果：
程序清单11.19，join_chk.c:
/* join_chk.c -- 拼接两个字符串，检查第 1 个 数组的大小 */
#include
#include
#define SIZE 30
#define BUGSIZE 13
char * s_gets(char * st, int n);
int main(void)
{
char flower[SIZE];
char addon[] = "s smell like old shoes.";
char bug[BUGSIZE];
int available;
puts("What is your favorite flower?");
s_gets(flower, SIZE);
if ((strlen(addon) + strlen(flower) + 1) <= SIZE)
strcat(flower, addon);
puts(flower);
puts("What is your favorite bug?");
s_gets(bug, BUGSIZE);
available = BUGSIZE - strlen(bug) - 1;
strncat(bug, addon, available);
puts(bug);
return 0;
}
char * s_gets(char * st, int n)
{
char * ret_val;
int i = 0;
ret_val = fgets(st, n, stdin);
if(ret_val)
{
while (st[i] != '\n' && st[i] != '\0')
i++;
if (st[i] == '\n')
st[i] = '\0';
else
while (getchar() != '\n')
continue;
}
return ret_val;
} 输出结果：
程序清单11.20，nogo.c:
/* nogo.c -- 该程序能否正常运行？ */
#include
#define ANSWER "Grant"
#define SIZE 40
char * s_gets(char * st, int n);
int main(void)
{
char try[SIZE];
puts("Who is buried in Grant's tomb?");
s_gets(try, SIZE);
while (try != ANSWER)
{
puts("No, that's wrong. Try again.");
s_gets(try, SIZE);
}
puts("That's right!");
return 0;
}
char * s_gets(char * st, int n)
{
char * ret_val;
int i = 0;
ret_val = fgets(st, n, stdin);
if(ret_val)
{
while (st[i] != '\n' && st[i] != '\0')
i++;
if (st[i] == '\n')
st[i] = '\0';
else
while (getchar() != '\n')
continue;
}
return ret_val;
} 输出结果：
程序清单11.21，compare.c:
/* compare.c -- 该程序可以正常运行 */
#include
#include // 提供 strcmp() 函数原型
#define ANSWER "Grant"
#define SIZE 40
char * s_gets(char * st, int n);
int main(void)
{
char try[SIZE];
puts("Who is buried in Grant's tomb?");
s_gets(try, SIZE);
while (strcmp(try, ANSWER) != 0)
{
puts("No, that's wrong. Try again.");
s_gets(try, SIZE);
}
puts("That's right!");
return 0;
}
char * s_gets(char * st, int n)
{
char * ret_val;
int i = 0;
ret_val = fgets(st, n, stdin);
if(ret_val)
{
while (st[i] != '\n' && st[i] != '\0')
i++;
if (st[i] == '\n')
st[i] = '\0';
else
while (getchar() != '\n')
continue;
}
return ret_val;
} 输出结果:
程序清单11.22，compback.c:
/* compback.c -- strcmp() 的返回值 */
#include
#include
int main(void)
{
printf("strcmp(\"A\", \"A\") is %d\n", strcmp("A", "A"));
printf("strcmp(\"A\", \"B\") is %d\n", strcmp("A", "B"));
printf("strcmp(\"B\", \"A\") is %d\n", strcmp("B", "A"));
printf("strcmp(\"C\", \"A\") is %d\n", strcmp("C", "A"));
printf("strcmp(\"Z\", \"a\") is %d\n", strcmp("Z", "a"));
printf("strcmp(\"apples\", \"apple\") is %d\n", strcmp("apples", "apple"));
return 0;
} 输出结果：
程序清单11.23，quit_chk.c:
/* quit_chk.c -- 某程序的开始部分 */
#include
#include
#define SIZE 80
#define LIM 10
#define STOP "quit"
char * s_gets(char * st, int n);
int main(void)
{
char input[LIM][SIZE];
int ct = 0;
printf("Enter up to %d lines (type quit to quit):\n", LIM);
while (ct < LIM && s_gets(input[ct], SIZE) != NULL &&
strcmp(input[ct], STOP) != 0)
{
ct++;
}
printf("%d strings entered\n", ct);
for (int i = 0; i < ct; i++)
puts(input[i]);
return 0;
}
char * s_gets(char * st, int n)
{
char * ret_val;
int i = 0;
ret_val = fgets(st, n, stdin);
if(ret_val)
{
while (st[i] != '\n' && st[i] != '\0')
i++;
if (st[i] == '\n')
st[i] = '\0';
else
while (getchar() != '\n')
continue;
}
return ret_val;
} 输出结果：
程序清单11.24，starsrch.c:
/* starsrch.c -- 使用 strncmp() */
#include
#include
#define LISTSIZE 6
int main(void)
{
const char * list[LISTSIZE] =
{
"astronomy", "astounding",
"astrophysics", "ostracize",
"asterism", "astrophobia"
};
int count = 0;
int i;
for (i = 0; i < LISTSIZE; i++)
if (strncmp(list[i], "astro", 5) == 0)
{
printf("Found: %s\n", list[i]);
count++;
}
printf("The list contained %d words beginning"
" with astro.\n", count);
return 0;
} 输出结果：
程序清单11.25，copy1.c:
/* copy1.c -- 演示 strcpy() */
#include
#include // 提供 strcpy() 函数原型
#define SIZE 40
#define LIM 5
char * s_gets(char * st, int n);
int main(void)
{
char qwords[LIM][SIZE];
char temp[SIZE];
int i = 0;
printf("Enter %d words beginning with q:\n", LIM);
while (i < LIM && s_gets(temp, SIZE))
{
if (temp[0] != 'q')
printf("%s doesn't begin with q!\n", temp);
else
{
strcpy(qwords[i], temp);
i++;
}
if (i < LIM)
printf("Please keep going: ");
}
puts("Here are the words accepted:");
for (i = 0; i < LIM; i++)
puts(qwords[i]);
return 0;
}
char * s_gets(char * st, int n)
{
char * ret_val;
int i = 0;
ret_val = fgets(st, n, stdin);
if(ret_val)
{
while (st[i] != '\n' && st[i] != '\0')
i++;
if (st[i] == '\n')
st[i] = '\0';
else
while (getchar() != '\n')
continue;
}
return ret_val;
} 输出结果：
程序清单11.26，copy2.c:
/* copy2.c -- 使用 strcpy() */
#include
#include
#define WORDS "beast"
#define SIZE 40
int main(void)
{
const char * orig = WORDS;
char copy[SIZE] = "Be the best that you can be.";
char * ps;
puts(orig);
puts(copy);
ps = strcpy(copy + 7, orig); // 将 orig 所指向的字符串拷贝到 copy + 7所在地址，包括'\0'
puts(copy);
puts(ps);
return 0;
} 输出结果：
程序清单11.27，copy3.c:
/* copy3.c -- 使用 strncpy() */
#include
#include
#define SIZE 40
#define TARGSIZE 7
#define LIM 5
char * s_gets(char * st, int n);
int main(void)
{
char qwords[LIM][SIZE];
char temp[SIZE];
int i = 0;
printf("Enter %d words beginning with q:\n", LIM);
while (i < LIM && s_gets(temp, SIZE))
{
if (temp[0] != 'q')
printf("%s doesn't begin with q!\n", temp);
else
{
strncpy(qwords[i], temp, TARGSIZE - 1);
qwords[i][TARGSIZE - 1] = '\0';
i++;
}
}
puts("Here are the words accepted:");
for (i = 0; i < LIM; i++)
puts(qwords[i]);
return 0;
}
char * s_gets(char * st, int n)
{
char * ret_val;
int i = 0;
ret_val = fgets(st, n, stdin);
if(ret_val)
{
while (st[i] != '\n' && st[i] != '\0')
i++;
if (st[i] == '\n')
st[i] = '\0';
else
while (getchar() != '\n')
continue;
}
return ret_val;
} 输出结果：
程序清单11.28，format.c:
/* format.c -- 格式化字符串 */
#include
#define MAX 20
char * s_gets(char * st, int n);
int main(void)
{
char first[MAX];
char last[MAX];
char formal[2 * MAX + 10];
double prize;
puts("Enter your first name:");
s_gets(first, MAX);
puts("Enter your last name:");
s_gets(last, MAX);
puts("Enter your prize money:");
scanf("%lf", &prize);
sprintf(formal, "%s, %-19s: $%6.2f\n", last, first, prize);
puts(formal);
return 0;
}
char * s_gets(char * st, int n)
{
char * ret_val;
int i = 0;
ret_val = fgets(st, n, stdin);
if(ret_val)
{
while (st[i] != '\n' && st[i] != '\0')
i++;
if (st[i] == '\n')
st[i] = '\0';
else
while (getchar() != '\n')
continue;
}
return ret_val;
} 输出结果：
程序清单11.29，sort_str.c:
/* sort_str.c -- 读入字符串，并排序字符串 */
#include
#include
#define SIZE 81 /* 限制字符串长度，包括 \0 */
#define LIM 20 /* 可读入的最多行数 */
void stsrt(char * strings[], int num); // strings 是指针的指针
char * s_gets(char * st, int n);
int main(void)
{
char input[LIM][SIZE]; /* 存储输入的数组 */
char * ptstr[LIM]; /* 内含指针变量的数组 */
int ct = 0; /* 输入计数 */
int k; /* 输出计数 */
printf("Input up to %d lines, and I will sort them.\n", LIM);
printf("To stop, press the Enter key at line's start.\n");
while (ct < LIM && s_gets(input[ct], SIZE) != NULL
&& input[ct][0] != '\0')
{
ptstr[ct] = input[ct]; /* 设置指针指向字符串 */
ct++;
}
stsrt(ptstr, ct); /* 字符串排序函数 */
puts("\nHere's the sorted list:\n");
for (k = 0; k < ct; k++)
puts(ptstr[k]); /* 排序后的指针 */
return 0;
}
/* 字符串-指针-排序函数 */
void stsrt(char * strings[], int num)
{
char * temp;
int top, seek;
for (top = 0; top < num - 1; top++)
for (seek = top + 1; seek < num; seek++)
if (strcmp(strings[top], strings[seek]) > 0)
{
temp = strings[top];
strings[top] = strings[seek];
strings[seek] = temp;
}
}
char * s_gets(char * st, int n)
{
char * ret_val;
int i = 0;
ret_val = fgets(st, n, stdin);
if(ret_val)
{
while (st[i] != '\n' && st[i] != '\0')
i++;
if (st[i] == '\n')
st[i] = '\0';
else
while (getchar() != '\n')
continue;
}
return ret_val;
} 输出结果：
程序清单11.30，mod_str.c:
/* mod_str.c -- 修改字符串 */
#include
#include
#include
#define LIMIT 81
void ToUpper(char *);
int PunctCount(const char *);
int main(void)
{
char line[LIMIT];
char * find;
puts("Please enter a line:");
fgets(line, LIMIT, stdin);
find = strchr(line, '\n'); // 查找换行符
if (find) // 如果地址不是 NULL
*find = '\0'; // 用空字符替换
ToUpper(line);
puts(line);
printf("That line has %d punctuation characters.\n", PunctCount(line));
return 0;
}
void ToUpper(char * str)
{
while (*str)
{
*str = toupper(*str);
str++;
}
}
int PunctCount(const char * str)
{
int ct = 0;
while (*str)
{
if (ispunct(*str))
ct++;
str++;
}
return ct;
} 输出结果：
程序清单11.31，repeat.c:
/* repeat.c -- 带参数的 main() */
#include
int main(int argc, char * argv[])
{
int count;
printf("The command line has %d arguments:\n", argc - 1);
for (count = 0; count < argc; count++)
printf("%d: %s\n", count, argv[count]);
printf("\n");
return 0;
} 输出结果：
程序清单11.32，hello.c:
/* hello.c -- 把命令行参数转换为数字 */
#include
#include
int main(int argc, char * argv [])
{
int i, times;
if (argc < 2 || (times = atoi(argv[1])) < 1)
printf("Usage: %s positive-number\n", argv[0]);
else
for (i = 0; i < times; i++)
puts("Hello, good looking!");
return 0;
} 输出结果：
程序清单11.33，strcnvt.c:
/* strcnvt.c -- 使用 strtol() */
#include
#include
#define LIM 30
char * s_gets(char * st, int n);
int main(void)
{
char number[LIM];
char * end;
long value;
puts("Enter a number (empty to quit):");
while (s_gets(number, LIM) && number[0] != '\0')
{
value = strtol(number, &end, 10);
printf("base 10 input, base 10 output: %ld, stopped at %s (%d)\n",
value, end, *end);
value = strtol(number, &end, 16);
printf("base 16 input, base 10 output: %ld, stopped at %s (%d)\n",
value, end, *end);
puts("Next number:");
}
puts("Bye!\n");
return 0;
}
char * s_gets(char * st, int n)
{
char * ret_val;
int i = 0;
ret_val = fgets(st, n, stdin);
if(ret_val)
{
while (st[i] != '\n' && st[i] != '\0')
i++;
if (st[i] == '\n')
st[i] = '\0';
else
while (getchar() != '\n')
continue;
}
return ret_val;
} 输出结果：
编程练习
题目1，方法：获取n个字符并存储。示例代码11_1.c:
#include
#define LEN 5
void getnchar(char *, int);
int main(void)
{
char str[LEN];
printf("Please input %d of characters: ", LEN - 1);
getnchar(str, LEN);
puts("The characters you input is:");
puts(str);
return 0;
}
void getnchar(char * ar, int n)
{
int i = 0;
while (i < n - 1)
*(ar + i++) = getchar();
*(ar + i) = '\0';
} 输出结果：
题目2，方法：获取n个字符（包括空格等）。示例代码11_2.c:
#include
#include
#define LEN 5
void getnchar(char *, int);
int main(void)
{
char str[LEN];
printf("Please input %d of characters: ", LEN - 1);
getnchar(str, LEN);
puts("The characters you input is:");
puts(str);
return 0;
}
void getnchar(char * ar, int n)
{
int i = 0;
while (i < n - 1)
if (isspace(*(ar + i++) = getchar()))
break;
*(ar + i) = '\0';
} 输出结果：
题目3、4，方法：保存字符串中第一个单词。示例代码11_3.c:
#include
#include
#define LEN 10
char * getword(char *, int);
int main(void)
{
char str[LEN];
printf("Please enter a words: ");
while (getword(str, LEN - 1) != NULL)
{
printf("The words you input is: ");
puts(str);
printf("You can input again: ");
}
return 0;
}
char * getword(char * st, int num)
{
int n = 0;
char ch;
//处理首字符
while ((ch = getchar()) != '&' && isspace(ch))
continue;
if (ch == '&')
return NULL;
else
{
*st++ = ch;
n++;
}
//首字符通过验证后处理其他字符
while ((ch = getchar()) != '&' && !isspace(ch) && n < num)
{
*st++ = ch;
n++;
}
*st = '\0';
if (ch != '\n')
while (getchar() != '\n')
continue;
return st;
} 输出结果：
题目5，方法：查找指定字符首次出现的地址。示例代码11_5.c：
#include
#include
#define LEN 40
char * s_gets(char *, int);
char * search_ch(char *, char);
int main(void)
{
char str[LEN];
char ch;
char * strs;
printf("Please input a string: ");
while (s_gets(str, LEN) != NULL && *str != '\n')
{
printf("Please input a character: ");
ch = getchar();
if (ch != '\n')
while (getchar() != '\n')
continue;
printf("The string you enter is: ");
puts(str);
printf("The character you enter is: ");
putchar(ch);
putchar('\n');
strs = search_ch(str, ch);
if (strs)
{
printf("The character first appear at ");
puts(strs);
}
else
printf("%c is not exist in the string\n", ch);
printf("You can input a string again: ");
}
return 0;
}
char * s_gets(char * st, int n)
{
char * ret_val;
char * find;
ret_val = fgets(st, n, stdin);
if (ret_val)
{
find = strchr(st, '\n'); //不需要处理换行符
// if (find)
// *find = '\0';
// else
if (!find)
while (getchar() != '\n')
continue;
}
return ret_val;
}
char * search_ch(char * st, char cha)
{
while (*st != '\0')
{
if (*st == cha)
return st;
st++;
}
return NULL;
} 输出结果：
题目6，方法：判断指定字符是否在字符串中。示例代码11_6.c:
#include
#include
#include
#define LEN 30
char * s_gets(char *, int);
bool search_ch(const char *, char);
int main(void)
{
char str[LEN];
char ch;
bool judge;
printf("Please input a string: ");
while (s_gets(str, LEN) != NULL && *str != '\0')
{
printf("Please input a character: ");
ch = getchar();
if (ch != '\n')
while (getchar() != '\n')
continue;
printf("The string you enter is: ");
puts(str);
printf("The character you enter is: ");
putchar(ch);
putchar('\n');
judge = search_ch(str, ch);
if (judge)
{
printf("%c is exist in the string\n", ch);
}
else
printf("%c is not exist in the string\n", ch);
printf("You can input a string again: ");
}
return 0;
}
char * s_gets(char * st, int n)
{
char * ret_val;
char * find;
ret_val = fgets(st, n, stdin);
if (ret_val)
{
find = strchr(st, '\n');
if (find)
*find = '\0';
else
while (getchar() != '\n')
continue;
}
return ret_val;
}
bool search_ch(const char * st, char cha)
{
while (*st != '\0')
{
if (*st == cha)
return true;
st++;
}
return false;
} 输出结果：
题目7，方法：截取字符串中的前n个字符。示例代码11_7.c:
#include
#include
#define LEN 30
char * s_gets(char *, int);
char * mystrncpy(char *, char *, int);
void clear(void);
int main(void)
{
char s1[LEN];
char s2[LEN];
int num;
int len;
printf("Please input a string: ");
while (s_gets(s1, LEN) != NULL && *s1 != '\0')
{
len = strlen(s1);
printf("Please input character id you want to copy: ");
while (scanf("%d", &num) != 1 || num < 1 || num > len)
{
printf("Wrong input, try again: ");
clear();
}
clear();
printf("The array of s2 is:%s\n", mystrncpy(s2, s1, num));
printf("You can input a string again: ");
}
return 0;
}
char * s_gets(char * st, int n)
{
char * ret_val;
char * find;
ret_val = fgets(st, n, stdin);
if (ret_val)
{
find = strchr(st, '\n');
if (find)
*find = '\0';
else
while (getchar() != '\n')
continue;
}
return ret_val;
}
char * mystrncpy(char * target, char * source, int n)
{
int i = 0;
while (*source != '\0' && i < n)
{
*(target + i) = *(source + i);
i++;
}
*(target + i) = '\0';
return target;
}
void clear(void)
{
while (getchar() != '\n')
continue;
} 输出结果：
题目8，方法：检测一个字符中是否包含另一个字符。示例代码11_8.c:
#include
#include
#define LEN 100
char * s_gets(char *, int);
char * search_str(char *, char *);
int main(void)
{
char str[LEN];
char str1[LEN];
char * strs, * strs1;
char * ptr;
printf("Please input the first string(no more than %d of characters): ",LEN - 1);
while ((strs = s_gets(str, LEN)) != NULL && *strs != '\0')
{
printf("\nPlease input the second string(no more than the first string): ");
while ((strs1 = s_gets(str1, LEN)) == NULL || *strs1 == '\0')
{
printf("Illegal input, try argin(at least one character): ");
}
ptr = search_str(str, str1);
if (ptr)
printf("\nThe string \"%s\" first appear at: \"%s\"\n", str1, ptr);
else
printf("\nThe string \"%s\" not exist in \"%s\".\n",str1, str);
printf("\nYou can input a string again(no more than %d of characters): ", LEN - 1);
}
return 0;
}
char * s_gets(char * st, int n)
{
char * ret_val;
char * find;
ret_val = fgets(st, n, stdin);
if (ret_val)
{
find = strchr(st, '\n');
if (find)
*find = '\0';
else
while (getchar() != '\n')
continue;
}
return ret_val;
}
char * search_str(char * st, char * st1)
{
int i, j;
int len_st, len_st1; //字符串长度
int num; //出现次数
int num_o;//完整出现次数
char * addr[LEN]; //每次出现地址
char * addr_o[LEN];//完整出现地址
char ch;//字符变量
len_st = strlen(st);
len_st1 = strlen(st1);
if (len_st < len_st1)
return NULL;
for (i = 0, j = 0, num = 0; i < len_st; i++)
{
if (st1[j] == st[i])
j++;
else if (*st1 == st[i]) // 如 abaab 中 ab
j = 1;
else
j = 0;
if (j == len_st1)
{
*(addr + num++) = (st + i) - (len_st1 - 1); //字符串起始位置
j = 0; //初始化j的值
i = i - len_st1 + 1; //一旦查找成功一次则只移动一个字符
}
}
for (i = 0, num_o = 0; i < num; i++)
if (((ch = *(*(addr + i) + len_st1)) ==' ' || ch == '\0') &&
((ch = *(*(addr + i) - 1)) ==' ' || *(addr + i) == st))
{
*(addr_o + num_o++) = *(addr + i);
}
if (num == 0)
return NULL;
printf("\n\"%s\" appear in \n\"%s\" \ntotally %d times\n", st1, st, num);
for (i = 0; i < num; i++)
printf("\n%dth time:\n%s\n", i + 1, *(addr + i));
printf("\n\"%s\" appear in \n\"%s\" \nintegrel totally %d times\n", st1, st, num_o);
for (i = 0; i < num_o; i++)
printf("\n%dth time:\n%s\n", i + 1, *(addr_o + i));
return * addr;
} 输出结果：
题目9，方法：将数组反序保存。示例代码11_9.c:
#include
#include
#define LEN 10
char * adstr(char *); // 倒序字符串
char * s_gets(char *, int);
int main(void)
{
char st[LEN];
char * strs;
printf("Please input a string(No more than %d of characters): ", LEN - 1);
while ((strs = s_gets(st, LEN)) != NULL && *strs != '\0')
{
adstr(st);
printf("After advert, the array of st is: ");
puts(st);
printf("You can input another string: ");
}
return 0;
}
char * adstr(char * str)
{
int len;
int i;
char ptr;
//int i, j;
//char * sts[LEN];
len = strlen(str);
//方法一
for (i = 0; i < len / 2; i++)
{
ptr = *(str + i);
*(str + i) = *(str + len - 1 - i);
*(str + len - 1 - i) = ptr;
}
//方法二
// for (i = len - 1, j = 0; i >= 0 ; i--)
// {
// *(sts + j++) = str + i;
// }
// for (i = 0; i < j; i++)
// printf("%c", **(sts + i));
// putchar('\n');
//
// return *sts;
return str;
}
char * s_gets(char * st, int n)
{
char * ret_val;
char * find;
ret_val = fgets(st, n, stdin);
if (ret_val)
{
find = strchr(st, '\n');
if (find)
*find = '\0';
else
while (getchar() != '\n')
continue;
}
return ret_val;
} 输出结果：
题目10，方法：删除字符串中的空格。示例代码11_10.c:
#include
#include
#define LEN 10
void dspace(char *);
char * s_gets(char *, int);
int main(void)
{
char st[LEN];
char * strs;
printf("Please input a string(No more than %d of characters): ", LEN - 1);
while ((strs = s_gets(st, LEN)) != NULL && *strs != '\0')
{
dspace(st);
printf("After delete space, the array of st is: ");
puts(st);
printf("You can input another string: ");
}
return 0;
}
void dspace(char * st)
{
char * ptr;
ptr = st;
while (*st)
{
if (*st != ' ')
*ptr++ = *st++;
else
st++;
}
*ptr = '\0';
}
char * s_gets(char * st, int n)
{
char * ret_val;
char * find;
ret_val = fgets(st, n, stdin);
if (ret_val)
{
find = strchr(st, '\n');
if (find)
*find = '\0';
else
while (getchar() != '\n')
continue;
}
return ret_val;
} 输出结果：
题目11，方法：根据选项处理字符串。该项目包含2个头文件和3个源文件。
str_pro.h:
#include
#include
#include
#include
#include
void show_menu(void);
char * s_gets(char *, int); //获取字符串
int get_strings(int, int, char (*)[]); //将最多m个最大长度为n的字符串读入str中
void pt_strings(int, int, char **, char (*)[]); //将指针的数组指向对应的字符串的地址
int first_len(char *); //计算字符串中第一个单词长度
void or_print(int, int, char(*)[]); //打印原始字符串列表
void as_print(int, char **); //ASCII打印字符串列表
void le_print(int, char **); //长度递增打印字符串列表
void fi_print(int, char **); //第一个单词递增打印 str_pro.c:
#include "str_pro.h"
#include "check.h"
void show_menu(void)
{
printf("****************************************\n");
printf("Please choose the operation:\n");
printf("a. Origin b. ASCII order\n");
printf("c. Upgrade d. First length\n");
printf("q. Quit\n\n");
}
char * s_gets(char * st, int n)
{
char * ret_val;
char * find;
ret_val = fgets(st, n, stdin);
if (ret_val)
{
find = strchr(st, '\n');
if (find)
*find = '\0';
else
while (getchar() != '\n')
continue;
}
return ret_val;
}
int get_strings(int m, int n, char (*str)[n])
{
int i;
char * ptr;
for (i = 0; i < m; i++)
{
printf("Now you can input %dth of string(EOF or Enter to quit): ", i + 1);
if ((ptr = s_gets(*(str + i), n)) != NULL && *ptr != '\0')
{
system("cls");
continue;
}
else
break;
}
system("cls");
return i;
}
void pt_strings(int num, int n, char ** pt, char (*source)[n])
{
int i;
for (i = 0; i < num; i++)
{
*(pt + i) = *(source + i);
}
}
int first_len(char * st)
{
int length = 0;
bool inword = false;
while (*st != '\0')
{
if (!isspace(*st) && inword == false)
{
inword = true;
length++;
}
if (!isspace(*st) && inword == true)
length++;
if (isspace(*st) && inword == true)
break;
st++;
}
return length;
}
void or_print(int num, int n, char(*str)[n])
{
int i;
for (i = 0; i < num; i++)
{
printf("The %dth of string: ", i + 1);
puts(*(str + i));
}
wait();
}
void as_print(int num, char ** pt)
{
int i, j;
char * temp;
for (i = 0; i < num - 1; i++)
for (j = i + 1; j < num; j++)
{
if (strcmp(*(pt + i), *(pt + j)) > 0)
{
temp = *(pt + j);
*(pt + j) = *(pt + i);
*(pt + i) = temp;
}
}
for (i = 0; i < num; i++)
{
printf("The %dth of string: ", i + 1);
puts(*(pt + i));
}
wait();
}
void le_print(int num, char ** pt)
{
int i, j;
char *temp;
for (i = 0; i < num - 1; i++)
for (j = i + 1; j < num; j++)
{
if (strlen(*(pt + i)) > strlen(*(pt + j)))
{
temp = *(pt + j);
*(pt + j) = *(pt + i);
*(pt + i) = temp;
}
}
for (i = 0; i < num; i++)
{
printf("The %dth of string: ", i + 1);
puts(*(pt + i));
}
wait();
}
void fi_print(int num, char ** pt)
{
int i, j;
char *temp;
for (i = 0; i < num - 1; i++)
for (j = i + 1; j < num; j++)
{
if (first_len(*(pt + i)) > first_len(*(pt + j)))
{
temp = *(pt + j);
*(pt + j) = *(pt + i);
*(pt + i) = temp;
}
}
for (i = 0; i < num; i++)
{
printf("The %dth of string: ", i + 1);
puts(*(pt + i));
}
wait();
}check.h:
#include
#include
#include
#include
#include
void wait(void);//暂停打印提示信息
void consumer(char *, int *);//清空缓冲区并保存清空的字符
bool character_check(char *, int *); //检测是否有非空字符并清空第一个非空字符及之前的缓冲区
char choose_check(int); //将输入限制在合法区间并返回输入值 check.c:
#include "check.h"
#include "str_pro.h"
void wait(void)
{
char ch;
printf("Enter to continue...");
while ((ch = getchar()) != '\n')
continue;
system("cls");
}
void consumer(char * wrong, int * n)
{
char cha;
while ((cha = getchar()) != '\n')
*(wrong + (*n)++) = cha;
}
bool character_check(char * wrong, int * n)
{
char ch2;
while ((ch2 = getchar()) != '\n') //第一个非空字符为回车，则读走回车
{
*(wrong + (*n)++) = ch2;
if (ch2 != '\t' && ch2 != ' ') //若第一个非空字符非回车，回车不被读走
return true;
}
return false;
}
char choose_check(int n)
{
char ch1;
char notice[n];
int num = 1;
int * count = #
show_menu();
printf("Enter a character to choose: ");
//防止第一个非空合法字符后出现第二个非空字符，例如assss
while (((ch1 = tolower(getchar())) != 'a' && ch1 != 'b' && ch1 != 'c' && ch1 != 'd' && ch1 != 'q') || character_check(notice, count) == true)
{
if (ch1 == ' ' || ch1 == '\n' || ch1 == '\t') // 使至少第一个非空字符被ch1获得
continue;
else if (character_check(notice, count) == true) //防止出现 assss 这样的输入，即之前非法，之后合法，以及清空非空白字符缓冲区
consumer(notice, count); //输入a2时判断返回false，不执行此步(此时所有字符包括回车均已被读走）
system("cls");
show_menu();
*notice = ch1;
printf("%s is illegal, try again: ", notice);
memset(notice, 0 ,sizeof(notice)); //初始化字符串数组
num = 1; //重置计数
}
return ch1;
}main.c:
#include "check.h"
#include "str_pro.h"
#define WRONG 200
#define ROW 10
#define COL 100
int main(void)
{
char * ptr[ROW]; //用于指向字符串地址的指针
char strings[ROW][COL]; //申请分配10个长度为100个字符的空间
char ch; //保存功能选项
int count; //用于存储输入多少个字符串
printf("Please input no more than %d of strings(First EOF or enter to quit):\n", ROW);
//申请空间数不必与操作空间数一致，但应该保证申请空间数大于等于操作数，否则将会越界
while ((count = get_strings(ROW, COL,strings)) != 0)
{
pt_strings(count, COL, ptr, strings);
while ((ch = choose_check(WRONG)) != 'q')
{
switch (ch)
{
case 'a':
or_print(count, COL, strings);
break;
case 'b':
as_print(count, ptr);
break;
case 'c':
le_print(count, ptr);
break;
case 'd':
fi_print(count, ptr);
break;
default:
printf("error.\n");
}
}
system("cls");
printf("Please input no more than %d of strings(First EOF or enter):\n", ROW);
}
return 0;
}输出结果：
题目12，方法：报告字符串中相关信息。示例代码11_12.c:
#include
#include
#include
int main(void)
{
int ch, words, upper, lower, punct, digit;
words = upper = lower = punct = digit = 0;
bool inword = false;
printf("Please input some graceful characters: ");
while ((ch = getchar()) != '&')
{
if (!isspace(ch) && inword == false)
{
inword = true;
words++;
}
if (isspace(ch) && inword == true)
inword = false;
if (isupper(ch))
upper++;
else if (islower(ch))
lower++;
else if (ispunct(ch))
punct++;
else if (isdigit(ch))
digit++;
}
printf("Words:%3d\n", words);
printf("Upper:%3d\n", upper);
printf("Lower:%3d\n", lower);
printf("Punct:%3d\n", punct);
printf("Digit:%3d\n", digit);
return 0;
} 输出结果：
题目13，方法：反序显示命令行参数的字符串。示例代码11_13.c:
#include
int main(int argc, char * argv[])
{
int i = 0;
if (argc < 2)
printf("Usage: %s\n", *argv);
else
{
printf("Words: ");
for (i = 1; i < argc; i++)
printf("%s ", *(argv + i));
putchar('\n');
printf("Reveted words: ");
for (i = argc - 1; i > 0; i--)
printf("%s ", *(argv + i));
}
putchar('\n');
return 0;
} 输出结果：
题目14，方法：命令行参数计算幂。示例代码11_14.c:
#include
#include
int main(int argc, char * argv[])
{
int i, exp;
double num, sum;
sum = 1.0;
if (argc != 3)
printf("Usage: %s,Input double number and integer", *argv);
else
{
num = atof(*(argv + 1));
exp = atoi(*(argv + 2));
if (exp == 0)
sum = 0;
else if (exp > 0)
{
for (i = 0; i < exp; i++)
sum *= num;
}
else
{
for (i = 0; i < -exp; i++)
sum *= num;
sum = 1 / sum;
}
printf("Sum = %g\n", sum);
}
return 0;
} 输出结果：
题目15，方法：判断输入字符串是否纯数字组成。示例代码11_15.c:
#include
#include
#include
#define LEN 20
char * s_gets(char *, int); //获取字符串
int myatoi(char *); //将字符转换为数字
int main(void)
{
char str[LEN];
printf("Please input a string(EOF to quit): ");
while (s_gets(str, LEN) != NULL)
{
printf("String %s convert to digital is %d\n", str, myatoi(str));
printf("You can enter another string(EOF to quit): ");
}
return 0;
}
char * s_gets(char * st, int n)
{
char * ret_val;
char * find;
ret_val = fgets(st, n, stdin);
if (ret_val)
{
find = strchr(st, '\n');
if (find)
*find = '\0';
else
while (getchar() != '\n')
continue;
}
return ret_val;
}
int myatoi(char * st)
{
int num = 0;
while (*st)
{
if (!isdigit(*st))
return 0;
else
num = num * 10 + (*st - '0');
st++;
}
return num;
} 输出结果：
题目16，方法：转换字符串并输出。示例代码11_16.c:
#include
#include
int main(int argc, char * argv[])
{
int ch;
int flag = 1;
char mode = 'p';
if (argc > 2)
{
printf("Usage: %s [-p | -u| -l]\n", *argv);
flag = 0;
}
else if (argc == 2)
{
if (**(argv + 1) != '-')
{
printf("Usage: %s [-p | -u| -l]\n", *argv);
flag = 0;
}
else
{
switch (*(*(argv + 1) + 1))
{
case 'p':
case 'u':
case 'l':
mode = *(*(argv + 1) + 1);
break;
default:
printf("Usage: %s [-p | -u| -l]\n", *argv);
flag = 0;
}
}
}
if (flag)
{
printf("Please input some characters: ");
while ((ch = getchar()) != '&' && ch != '\n')
{
switch (mode)
{
case 'p':
putchar(ch);
break;
case 'u':
putchar(toupper(ch));
break;
case 'l':
putchar(tolower(ch));
break;
}
}
}
return 0;
} 输出结果：
