C语言学生信息录入与密码校验程序运行故障问题求解

• 字符串比较逻辑完全错误：C语言中不能用==直接比较两个字符串的内容，该运算符只会对比两个字符串的首内存地址，永远不会相等（除非指向同一块内存）；你写的psswrd == "%s%s",yr, stid属于语法逻辑完全错误，逗号表达式最终仅会取最后一个操作数stid的值参与判断，完全达不到拼接后对比的效果。
• 未提前拼接生成正确密码：你没有将yr（年级班级）和stid（学号）拼接为完整的正确密码字符串，无法直接和用户输入的密码做对比。
• 循环逻辑写反：当前代码判断条件成立时进入循环提示验证失败，你应该是密码不匹配时才进入循环要求重新输入，逻辑完全颠倒。
• printf参数不匹配：输出学生ID的语句printf("Student ID: %s%s\n",stid );写了2个%s占位符，但只传入了1个参数，会触发未定义行为，输出乱码。
• fgets读取的字符串末尾会残留换行符\n，输出个人信息时会出现不必要的空行。

#include <stdio.h>
#include <string.h>

// 处理fgets残留的换行符
void trim_newline(char *str) {
    int len = strlen(str);
    if (len > 0 && str[len-1] == '\n') {
        str[len-1] = '\0';
    }
}

int main (){
    char fname[25];
    char lname[10];
    char addr[50];
    char yr[10];
    char cr[50];
    char stid[15];
    char correct_pwd[25]; // 存储拼接后的正确密码
    char psswrd[50];

    printf("Welcome to the Code! \n");
    printf("Please Input your First Name: ");
    fgets(fname, 25, stdin); 
    trim_newline(fname);
    printf("Please Input your Last Name: ");
    fgets(lname, 10, stdin);
    trim_newline(lname);
    printf("Please Input your address: ");
    fgets(addr, 50, stdin);
    trim_newline(addr);
    printf("Please Input your Course: ");
    fgets(cr, 50, stdin);
    trim_newline(cr);
    printf("Please Input your College Year & Section: ");
    scanf("%s", yr);
    printf("Please Input your Student ID: ");
    scanf("%s", stid);

    // 拼接生成正确密码
    strcpy(correct_pwd, yr);
    strcat(correct_pwd, stid);

    printf("\nYour Details:\n");
    printf("First Name: %s\n", fname);
    printf("Last Name: %s\n", lname);
    printf("Address: %s\n", addr);
    printf("College Year: %s\n", yr);
    printf("Course: %s\n", cr);
    printf("Student ID: %s\n", stid);
    printf("Your Password: %s\n", correct_pwd);

    printf("Please Input your New Password to Get Verified: ");
    scanf("%s", psswrd);
    printf("You Have Inputted: %s\n", psswrd);

    // 密码不匹配就循环重输
    while (strcmp(psswrd, correct_pwd) != 0)
    {
        printf("Verification Failed. \n");
        printf("Please Input Your Password: ");
        scanf("%s", psswrd);
        printf("You Have Inputted: %s\n", psswrd);
    }
    printf("Verification Successful! \nThank you for Using the Code!");

    return 0;   
}

内容的提问来源于stack exchange，提问作者Meat_Salad