重復菜單並提示用戶是否在C中輸入了無效選擇

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');
}

這是我的基本想法，但我無法提示錯誤的選擇並重復菜單。 輸入錯誤的選擇時，輸出如下：例如，輸入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

看一下以下更改：將您的scanf（）更改為

scanf(" %c",&choice);

％c之前的空格將確保所有特殊字符（包括換行符）都將被忽略。每次在緩沖區中沒有換行符時，scanf都會從中讀取新行，並且您會發現外觀不符合預期。

此后，請確保一旦擊中默認大小寫，您就需要從while（）循環中斷開。

    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

第一件事， break; 在每種情況下，僅適用您選擇的情況。 要解決2次打印問題，只需在scanf("%c", &choice);更改％c scanf("%c", &choice); 到％s >> scanf("%s", &choice);

這是代碼：

 #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');
}