如何使循环不断地询问用户输入，直到输入停止程序的给定字符？答案

【问题标题】：How to make a loop continuously keep asking for user input until a given character is entered that stops the program?如何使循环不断地询问用户输入，直到输入停止程序的给定字符？
【发布时间】：2022-09-29 04:05:50
【问题描述】：

我有这个程序：

int main(void){
    int x, number, factorial;

// The objective of this program is to compute the factorial
// for a user inputted number, stopping once \"-1\" is entered.

    printf(\"Please enter a positive number for factorial calculation (-1 to end) :\");
    scanf(\"%d\", &number);
        
    for (x = 1; x <= number; x++){
        factorial *= x;
        if (x == -1){
            break;
        }
    }   
    printf(\"factorial for %d is %d\", number, factorial);
    
    
}

应该像这样输出：

Please enter a positive number for factorial calculation (-1 to end) :4
factorial for 4 is 24
Please enter a positive number for factorial calculation (-1 to end) :6
factorial for 6 is 720
Please enter a positive number for factorial calculation (-1 to end) :8
factorial for 8 is 40320
Please enter number for factorial calculation (-1 to end) :-1

但我不断得到这个（在两次不同的运行中）：

Please enter a positive number for factorial calculation (-1 to end) :4
factorial for 4 is 24

Please enter a positive number for factorial calculation (-1 to end) :-1
factorial for -1 is 1

我怎样才能让它继续要求更多的数字，直到我输入-1？另外，为什么在这里输入 -1 给我它的阶乘而不是停止循环？

语言不是c#，应该是c/c++...

标签： c

【解决方案1】：

您可以将阶乘计算包装在这样的循环中：

    int number;
    int factorial = 1;
    while(true) {
        printf("Please enter a positive number for factorial calculation (-1 to end) :");
        scanf("%d", &number);
        if (number == -1)
            break; // or just return as you need
        for (x = 1; x <= number; x++){
            factorial *= x;
        }   
        printf("factorial for %d is %d", number, factorial);
        factorial = 1;
    }

在这种情况下，您将收到数字作为输入，然后开始检查用户输入的内容。

在您的代码中，您在 for 循环中检查 x 变量是否不同于 -1，但是当您开始循环时将 1 分配给 x 时，永远不会满足该条件。在这种情况下，您应该检查number，但这并不完全正确。

【讨论】：

【解决方案2】：

使用While loop 并检查用户输入后的值，看看是否需要跳出循环：

int main(void){
    int x, number, factorial;

// The objective of this program is to compute the factorial
// for a user inputted number, stopping once "-1" is entered.
 
    while (true){
        printf("Please enter a positive number for factorial calculation (-1 to end) :");
        scanf("%d", &number);
        
        if (number == -1){
            break;
        }
        for (x = 1; x <= number; x++){
            factorial *= x;                
        }   
        printf("factorial for %d is %d", number, factorial);
    }
    
}

【讨论】：