如果用户在 C 中输入了无效的选择，则重复菜单并提示

Question

void menu(){ 
printf("\n"); 
printf("1. Convert integers in decimal number system to binary numbers \n"); 
printf("2. Compute a consecutive square root expression \n"); 
printf("3. Solve a quadratic equation \n"); 
printf("4. Print something fun \n"); 
printf("q. Quit\n \n"); 
printf(" Enter your choice: ");
}
main () {   
char choice;
do { 
    menu();
    scanf("%c", &choice);
    switch (choice){ 
         case '1':
             ...
         case '2':
             ....
         case '3':
             ...
         case '4':
             ....
        default: 
            printf("Wrong choice. Please enter again: "); 
            break; 
    }

}
while (choice != 'q');
}

这是我的总体思路，但我无法让它提示错误的选择并重复菜单。当我输入错误的选择时，输出如下： 比如我输入5：

  Enter your choice: 5
  Wrong choice, please enter again:
  1. Convert integers in decimal number system to binary numbers
  2. Compute a consecutive square root expression
  3. Solve a quadratic equation
  4. Print something fun
  q. Quit
  Enter your choice: (this is where I get to input)

Answer 1

看看下面的变化： 将您的 scanf() 更改为

scanf(" %c",&choice);

%c 之前的空格将确保忽略包括换行符在内的所有特殊字符。如果没有这个，每次缓冲区中有一个换行符，scanf 从它读取，你会发现你的外观没有按预期工作。

在此之后，请确保一旦遇到默认情况，您需要中断 while() 循环。

    do {  
          menu();
          scanf(" %c", &choice);
          switch (choice){ 
             case '1':
                break;
             case '2':
                break;
             case '3':
                break;
             case '4':
                break;
             default:
               {   
                  printf("Wrong choice. Please enter again: "); 
                  break; 
               }   
          }   
   }   
   while (choice != 'q');

Answer 2

首先，在每种情况下都输入break;，这样只有您选择的情况才会适用。要解决打印 2 次的问题，只需将 scanf("%c", &choice); 中的 %c 更改为 %s >> scanf("%s", &choice);

这是代码：

 #include <stdio.h> 
void menu(){ 
printf("\n"); 
printf("1. Convert integers in decimal number system to binary numbers \n"); 
printf("2. Compute a consecutive square root expression \n"); 
printf("3. Solve a quadratic equation \n"); 
printf("4. Print something fun \n"); 
printf("q. Quit\n \n"); 
printf(" Enter your choice: ");
}
main () {   
    char choice;
    do { 
        menu();
        scanf("%s", &choice);
        switch (choice){ 
            case '1':
                printf("1 \n");
                break;
            case '2':
                printf("2 \n");
                break;
            case '3':
                printf("3 \n");
                break;
            case '4':
                printf("4 \n");
                break;
             case 'q': 
                break;
            default: 
                printf("Wrong choice. Please enter again: "); 
                break; 
        }

    }
    while (choice != 'q');
}