C语言：判断最长重复字符串

#include <string.h>
#include <stdio.h>
#include<stdlib.h>
#include<time.h>
char *str_out(char * str_);
char *mid(char * ,int ,int);
#define MON1  1
const int MAX = 3;
int main(int argc, char *argv[])
{
char num[100]="NULL",*p="\0",s[]="ok",p_str[]="abcdefghijklmnopqrstuvwxyz0123456789";
int tongji=0;
printf("你好你要判断的最长重复字符串!\r\n");
scanf("%s",&num);
printf("最长字符为：%s\n",str_out(num));
getchar();
return 0;
}
char *str_out(char * str_){
char *p=NULL,*temp=NULL,str1[100]="\0",str2[100]="\0",str3[100]="\0";
int i=0,j=0,k=0,str_Len=0,str_changdu=1,str_chongfu=1;
p=str1;temp=str2;
str_Len=strlen(str_);
for(i=1;i<str_Len;i++)
{
str_changdu=1;
for(k=1;(k+i)<=str_Len;k++)
{
strcpy(p,mid(str_,k,i));
//printf("%s\n",p);
str_chongfu=1;
for(j=k+i;(j+i)<=(str_Len+1);j++)
{
strcpy(temp,mid(str_,j,i));
//printf("===%s\n",temp);
if(strcmp(p,temp)==0)
{
str_chongfu++;
if(str_chongfu>str_changdu)
{str_changdu=str_chongfu;strcpy(str3,p);
printf("最长字符为：%s,重复%d次\n",str3,str_chongfu);
}
}
}
}
}
return str3;
}
char *mid(char * str_,int start,int end){//自己写的MID函数
int i;char s[50]="\0";
for (i=0;i<end;i++){
s[i]=str_[start+i-1];
}
//puts(s);
return s;
}