几个字符串函数的实现

strlen

int strlen( const char *str ) 

{
　assert( strt != NULL ); 
　int len;
　while( (*str++) != '\0' )
　{
　　len++;
　}
　return len;
}

 strcpy

char * strcpy( char *strDest, const char *strSrc )
{
　assert( (strDest != NULL) && (strSrc != NULL) );
　char *address = strDest;
　while( (*strDest++ = * strSrc++) != ‘\0’ );
　　return address;
}

 strcmp

int strcmp(const char *s1,const char *2)
{
	assert(s1 !=NULL && s2 != NULL);
        while(*s1 == *s2 && *s1)
        {
                s1++;
                s2++;
        }
        if(*s1 == '\0' && *s2 == '\0')
                return 0 ;
        else
                return *s1 - *s2;

}

 判断字符串回文

int cycle(char *s)
{
        char *h, *t;
        for(h=s,t=&s[strlen(s)-1];t>h;h++,t--)
        {
                if(*h != *t)
                        break;
        }
        return h >= t;
}

int iscycle(char * s, int len)
{
        if(len <= 1)
                return 1;
        else if(s[0] == s[len-1])
                return iscycle(s+1,len-2);
        else
                return 0;
}