整型提升 和 位操作

http://blog.chinaunix.net/uid-26758020-id-3143673.html  现在正在学习，看见这个博客真是太好了。。。

 1.#对计算机不存在有无符号数，只是对单元数据的解释不同，存储的数据不变
 #include <stdio.h>

 int main(int argc, const char *argv[])
 {
     int n=-1;
     printf("%d %u 0x%x\n",n,n,n);
     return 0;
 }
 2.#当前的编译器把char类型解释为有符号数，char的范围是-128～127
   #打印else后的语句
 #include <stdio.h>

 int main(int argc, const char *argv[])
 {
     char c=128;
     //char=int 将int截断为char型
     if(c==128)
     //将c进行int型提升，进行符号位扩展，前24位为1，底8位为10000000
         printf("c==128\n");
     else
         printf("c!=128\n");
     return 0;
 }
 3.#类型的扩展
   #打印else后的语句
 #include <stdio.h>

 int main(int argc, const char *argv[])
 {
     unsigned int n=6;
     int m=-10;
     if((m+n)<n)
     //m扩展为unsigned型，进行符号位扩展，前24位为1，后8位为256-10原码的形式
         printf("m+n<n\n");
     else
         printf("m+n>n=n\n");
     return 0;
 }
 4.#验证-2147483648,int型无法存储在内存内
 #include <stdio.h>

 int main(int argc, const char *argv[])
 {
     printf("%d\n",-2147483648); //有警告，内存不存储该数
     printf("%d\n",-2147483647-1); //无警告，进行算数运算，均在int型范围之内
     return 0;
 }
 5.#验证是否越界和是否进行数据类型转换，打印a>b
 #include <stdio.h>

 int main(int argc, const char *argv[])
 {
     int a=-2147483647;
     int b=-2147483647-1;
     if(a>b)
         printf("a>b\n",a,b);
     if(-a<-b) //b越界，进行整形转换为0
         printf("-a<-b\n");

     a=2147483647;
     b=-1;
     if((a-b)>0) //a-b越界，进行整形转换为0
         printf("(a-b)>0\n");
     return 0;

 }
 6.#不能对浮点数进行取反操作，有错误
 #include <stdio.h>

 int main(int argc, const char *argv[])
 {
     float f=3.14;
     ~f;
     return 0;
 }
 7.#输入一个数，实现对0～3位清0，在对0～3位取反，和4～7位置1
 #include <stdio.h>

 int main(int argc, const char *argv[])
 {
     unsigned n;
     printf("n=0x");
     scanf("%x",&n);
     printf("(0~3)clean=%#x\n",n&0xfffffff0);
     printf("(4~7)set=%#x\n",n|0xf0);
     printf("(0~3)opp=%#x\n",n^0xf);
     return 0;
 }
 8.#s+=5并不总是等价于s=s+5
 #include <stdio.h>

 int main(int argc, const char *argv[])
 {
     int i=0,a[10]={1,2,3,4,5};
     a[i++]+=5; //与a[i++]=a[i++]+5不等价
     printf("%d\n",a[0]);
     return 0;
 }
 9.#用位操作判断一个数是奇数还是偶数
 #include <stdio.h>

 int main(int argc, const char *argv[])
 {
     int n;
     printf("n=");
     scanf("%d",&n);
     if(n&1)
         printf("%d is a odd\n",n);
     else
         printf("%d is a even\n",n);
     return 0;
 }
 10.#通过位运算将整形数据的某些位清0和某些位置1
    #cleanbits(unsigned int n,int start,int end)
    #setbits(unsigned int n,int start,int end)
 #include <stdio.h>

 unsigned cleanbits(unsigned n,int start,int end)
 {
     return n&(((~0<<(end-start+1))<<start)|~(~0<<start));
 }
 unsigned setbits(unsigned n,int start,int end)
 {
     return n|(~(~0<<(end-start+1))<<start);
 }
 int main(int argc, const char *argv[])
 {
     unsigned n;
     int s,e;
     printf("num0x start end\n");
     scanf("%x %d %d",&n,&s,&e);
     if(s>=e||s<0||e>32)
         printf("error s to e\n");
     printf("clean(s,e)=%#x\n",cleanbits(n,s,e));
     printf("set(s,e)=%#x\n",setbits(n,s,e));
     return 0;
 }
 11.#通过位运算获取某个整形术的某些位
    #getbits(unsigned int n,int start,int end)
 #include <stdio.h>

 unsigned getbits(unsigned n,int start,int end)
 {
     return (n>>start)&(~(~0<<end-start+1));
 }

 int main(int argc, const char *argv[])
 {
     unsigned n;
     int start,end;
     printf("num0x start end\n");
     scanf("%x %d %d",&n,&start,&end);
     if((start>=end)|(start<0)|(end>31))
         printf("error start or end\n");
     printf("(%d~%d)getbits(%x)=%#x\n",start,end,n,getbits(n,start,end));
     return 0;
 }
 12.#若有unsigned short a=0x1234,b=0x5678,获取a的高字节，b的低字节组成新值，结果为：0x1278
 #include <stdio.h>

 int main(int argc, const char *argv[])
 {
     unsigned short int a,b,c;
     printf("a b(0x):");
     scanf("%hx %hx",&a,&b);
     c=(a&0xff00)|(b&0xff);
     printf("new_num=0x%hx\n",c);
     return 0;
 }
 13.#实现unsigned short数据的字节交换
 #include <stdio.h>

 unsigned short swap(unsigned short n)
 {
     return (n>>8)|(n<<8);
 }

 int main(int argc, const char *argv[])
 {
     unsigned short n;
     printf("n=0x:");
     scanf("%hx",&n);
     printf("swap(0x%hx)=0x%hx\n",n,swap(n));
     return 0;
 }
 14.#求unsigned int型数据中有多少个1
 #include <stdio.h>

 int main(int argc, const char *argv[])
 {
     unsigned n;
     int i,cnt=0;
     printf("n=0x");
     scanf("%x",&n);
     for (i = 0; i < 32; i++)
     {
         if(n&1)
             cnt++;
         n=n>>1;
     }
     printf("cnt=%d\n",cnt);
     return 0;
 }
 15.#实现unsigned int型数据的二进制打印
 #include <stdio.h>

 int main(int argc, const char *argv[])
 {
     unsigned n;
     int i;
     printf("n=0x");
     scanf("%x",&n);
     printf("binary=");
     for (i = 31; i >= 0; i--)
     {
         if((i+1)%8==0)
             printf(" ");
         printf("%u",(n>>i)&1);
     }
     printf("\n");
     return 0;
 }
 16.#通过位操作实现字母的大小写转化
 #include <stdio.h>

 int main(int argc, const char *argv[])
 {
     char ch;
     printf("ch=");
     scanf("%c",&ch);
     printf("%c\n",ch^0x20);
     return 0;
 }
 17.#使用位操作实现整数的乘法
 #include <stdio.h>

 int main(void)
 {
     int m, n, i, result = 0;;

     scanf("%d %d", &m, &n);

     for(i = 0; i < 32; i++)
         if((n >> i) & 0x01)
             result += (m << i);

     printf("%d * %d = %d\n", m, n, result);
     return 0;
 }
 18.#位操作实现循环左移、右移
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>

 unsigned shift_left(unsigned n, int bits)
 {
     return (n << bits) | (n >> (32 - bits));
 }

 unsigned shift_right(unsigned n, int bits)
 {
     return (n >> bits) | (n << (32 - bits));
 }

 int main(int argc, char *argv[])
 {
     char *savep;

     printf("left:0x%x\n", shift_left(strtol(argv[1], &savep, 16), atoi(argv[2])));
     printf("right:0x%x\n", shift_right(strtol(argv[1], &savep, 16), atoi(argv[2])));
     return 0;
 }
 19.#使用位操作的知识先数组中保存26个没有重复的英文字母
 方法1：
 #include <stdio.h>

 int main(int argc, const char *argv[])
 {
     int flag=0,n,i;
     char str[26];
     srand(time(NULL));
     while(flag!=0x3ffffff)
     { n=rand()%26;
         if(((flag>>n)&0x01)==0)
         {
             str[n]=n+'a';
             flag|=0x01<<n;
         }
     }
     for (i = 0; i < 26; i++)
     {
         printf("%c ",str[i]);
     }
     printf("\n");
     return 0;
 }
 方法2：
 #include <stdio.h>
 #include <stdlib.h>
 #include <time.h>

 int main(void)
 {
     char letter[26];
     int tmp, i, j, flag = 0;

     srand(time(NULL));
     for(i = 0; i < 26;){
         tmp = rand() % 26;
         if(((flag >> tmp) & 0x01) == 0){
             letter[i++] = tmp + 'a';
             flag |= (0x01 << tmp);
         }
         for(j = 31; j >= 0; j--)
             printf("%d", (flag >> j) & 0x01);
         printf("\n");
     }

     for(i = 0; i < 26; i++)
         printf("%c ", letter[i]);
     printf("\n");
     return 0;
 }