《c程序设计语言》读书笔记-5.5-指针实现strncpy，strncat，strncmp

#include <stdio.h>
#include <math.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include <curses.h>
void strncpy_(char *s,char *t,int n)
{
    while(*t && n-- > 0)
        *s++ = *t++;
    while(n-- > 0)
        *s++ = '\0';
}
void strncat_(char *s,char *t,int n)
{
    while(*s)
        s++;
    while((*s++ = *t++) && n-- > 0)
        ;
}
int strncmp_(char *s,char *t,int n)
{
    for( ; *s == *t;s++,t++)
        if(*s == '\0' || --n <= 0)
            return 0;
    return *s - *t;
}
int main()
{
    char *c = "Ilove you!";;
    char *p = "Ilpe ni!" ;

    int n = 3;
    int i;

    i = strncmp_(c,p,n);

    printf("%d",i);

    return 0;

}

主函数调用strncmp，该函数返回字符串ASCII码差值。