#include <stdio.h>
#include <string.h>typedef struct usr{char unm[21];char pwd[21];
}user;int main(int argc, const char *argv[])
{FILE* userfile=fopen("./user_tible.txt","r");printf("輸入username:");user u;scanf("%s",u.unm);printf("輸入password:");scanf("%s",u.pwd);char name[21];fgets(name,sizeof(name),userfile);int len=strlen(name);if(name[len-1]=='\n'){name[len-1]='\0';}for(int i=0;i<strlen(name);i++){if(name[i]!=u.unm[i]){puts("用戶名錯誤");return -1;}}char pwd[21];fgets(pwd,sizeof(pwd),userfile);int len2=strlen(pwd);if(pwd[len2-1]=='\n'){pwd[len2-1]='\0';}for(int i=0;i<strlen(pwd);i++){if(pwd[i]!=u.pwd[i]){puts("密碼錯誤");puts(pwd);return -1;}}puts("登錄成功");return 0;
}

作業:拷貝