字符串操作函数（面试必备）

#include <stdio.h>
#include <stdlib.h>

//strcpy
char* strcpy(char* dest,const char* src)
{
    char* tmp = dest;
    while((*dest++ = *src++) != '\0')
        ;
    return tmp;
}

//strcmp
int strcmp(const char* cs,const char* ts)
{
    register signed char res;    //register声明，尽量存到cpu内部寄存器
    while(1)
    {
        if((res=*cs-*ts++)!=0||!*cs++)    //!*cs++说明一个字符串结束符：'\0'或者是 0
            break;
    }
    return res;
}

int main()
{
    char* a = "abcd";
    char b[256];

    //string copy
    strcpy(b,a);
    printf("string a is %s! \n",a);
    printf("string b is %s! \n",b);

    if(!strcmp(a,b))
        printf("a is equeue with b! \n");
    else
        printf("a is not equeue with b! \n");

    return 0;
}