11_栈的递归实例2---strlen实现

#include <stdio.h>int strlen(const char* s){    if( s == NULL )    {        return -1;    }    else if( *s == '\0' )    {        return 0;    }    else    {        return strlen(s+1) + 1;    }}int main(){    printf("strlen(\"12345\") = %d\n", strlen("12345"));    printf("strlen(NULL) = %d\n", strlen(NULL));    printf("strlen(\"\") = %d\n", strlen(""));    return 0;}