C++str类函数问题，求解！

 void str_cat(char*p1,char*p2)
{
    while (*p1 != '\0') p1++;
    int i = 0;
    while (p2[i++] != '\0')
    {
        *p1 = p2[i - 1];p1++;
    }
    *p1 = '\0';
}
int str_cmp(char*p1,char*p2)
{
    while (*p1 != '\0' && *p2 != '\0')
    {
        if (*p1 != * p2) return *p1 - *p2;
        p1++;p2++;
    }
    return *p1 - *p2;
}
int str_len(char*p1,char*p2)
{
    int n = 0;
    while (*p1 != '\0') { p1++; n++; }
    while (*p2 != '\0') { p2++; n++; }
    return n;
}
int main()
{
char s1[100]="hello ";
char s2[]="world!";
str_cat(s1, s2);
printf("%s\n", s1);
int n = str_cmp("aaa", "ab");
printf("%d\n", n);
n = str_len("aaa", "ab");
printf("%d\n", n);
}

*p1=str1[s]; 什么鬼? 应该是p1 = str1吧
str_cmp[p1,p2];这是什么情况，方括号？
。。。
问题多，你直接看修改后的代码吧

 #include <iostream>
#include <string.h>
using namespace std;
void str_cat(char*p1,char*p2);
int str_cmp(char*p1,char*p2);
int str_len(char*p1);

int main()
{
    const int s=20;
    char str1[s];
    char str2[s];
    cin.getline(str1,s);
    cin.getline(str2,s);
    char* p1,*p2;
    p1=str1;
    p2=str2;
    str_cat(p1,p2);
    str_cmp(p1,p2);
    str_len(p1);
}
void str_cat(char*p1,char*p2)
{cout<<strcat(p1,p2);}

int str_cmp(char*p1,char*p2)
{cout<<strcmp(p1,p2);
return 0;}
int str_len(char* p)
{return strlen(p);}

http://codepad.org/oZzuKv6v

hello world!
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