#include<stdio.h>
#include<string.h>
#define MAX_SIZE 50
#define USERNAME "laowang"
#define QQ "844866571"
#define WEIXIN "zhognhuaxiaozi"
 void main ()
 {
     char username[MAX_SIZE],qq[MAX_SIZE],weixin[MAX_SIZE];
     printf("权限认证\n");
     do{
         printf("请输入我的网名\n");
         scanf("%s,username");
     }
     while(strcmp(username,USERNAME)!=0);
     


     do{
         printf("请输入我的QQ\n");
         scanf("%s,qq");
     }
     while(strcmp(qq,QQ)!=0);

 
     do{
         printf("请输入我的微信\n");
         scanf("%s,weixin");
     }
     while(strcmp(weixin,WEIXIN)!=0);
 }

为什么一运行的时候就停止了你？

scanf("%s,username");           //scanf("%s",username);  引号的位置