【C语言笔记】<十七>指针数组和指针类型的特点

指针数组

int main(int argc, const char * argv[]) {
    
    /*
    char str1[] = "lnj";
    char str2[] = "lmj";
    char str3[] = "jjj";
    char str4[] = "lk";
    
    char strs[4][20] =
    {
        "lnj",
        "lmj",
        "jjj",
        "lk"
    };
     */
    
    char *str1 = "lnj";
    char *str2 = "lmj";
    char *str3 = "jjj";
    char *str4 = "lk";
    
    
    // 定义数组的格式: 元素类型 数组名称[元素的个数]
//    int  a = 10;
//    int  b = 20;
//    int nums[2] = {10 , 20};
    
    char *names[4] =
    {
        "lnj",
        "lmj",
        "jjj",
        "lk"
    };
    
    for (int i = 0; i < 4; i++) {
        printf("names[%i] = %s\n", i , names[i]);
    }
    
    
    
    return 0;
}

指针类型的特点

void change();
void change2();
void change3(int values[]);
void change4(int *p);
char *demo();
char *demo2();

int main(int argc, const char * argv[]) {
    /*
     只要是数据类型就具备3个特点
     1.可以用来定义变量
     2.可以用来作为形参的类型
     3.作为返回值
     */
    /*
    int num = 10;
    change(num);
    printf("num = %i\n", num);
    
//    char *name = "lnj";
//    change2(name);
    
    int nums[] = {1, 3, 5};
//    change3(nums); // 数组名就是数组的地址
    change4(nums); // 数组名就是数组第0个元素的地址
    printf("nums[0] = %i\n", nums[0]);
     */
    
    char *name = demo();
    printf("name = %s\n", name);
    
    char *name2 = demo2();
    printf("name2 = %s\n", name2);
    
    return 0;
}

char *demo2()
{
    char name[]= "lnj";
    return name;
}

char *demo()
{
    char *name = "lnj";
    return name;
}

void change4(int *p)
// int *p = nums; == int *p = &nums; == int *p = &nums[0]
// int *p; p = nums;  p == nums;
{
    p[0] = 998;
}
// 不专业
void change3(int values[])
{
    values[0] = 998;
}

/*
void change2(char *p)
{
    *p = "lmj";
}
 */

void change(int value)
{
    value = 55;
}

实现strlen函数

#include 
int myStrlen(char *str);
int myStrlen2(char *str);
int myStrlen3(char *str);

int main(int argc, const char * argv[]) {
    // 要求自己实现strlen函数
    char *name = "lnj";
//    size_t size = strlen(name);
    int size =myStrlen3(name);
    printf("size = %i\n", size);
    return 0;
}


int myStrlen3(char *str)
{
    int count = 0;
    // \0 ascii 0 // 0代表假 1真
    while (*str++)count++;
    
    return count;
}

int myStrlen2(char *str)
{
    int count = 0;
    //    *str == str[0]
    while (*str++ != '\0') {
        count++; // 1
//        str = str + 1; // str == str[1]
//        str++; // ++可以在变量名前, 也可以在变量名后
    }
    return count;
}

int myStrlen(char *str)
{
    int count = 0;
    while (str[count] != '\0') {
        count++;
    }
    return count;
}