c - 输入数字错误时C中的跳转代码

Question

我有一个代码。想法是当我需要输入数字但我输入非数字字符时，检查错误并要求我输入工作数字，或者继续或中断。但它会跳过不输入数字的代码。这是代码:

int EnterNumber(){
    int number;
    printf("Enter your's number:");
    if(!scanf("%d", &number)){
        puts("Keypress don't number!"); 
        int choose = 0;
        puts("Work:\n\t1. Continue 2. Break \nYour's number will choose:");                 
        while(!scanf("%d", &choose)){   // here it jumped.I cann't enter number!
            switch(choose){
                case 1: 
                    EnterNumber();
                    break;
                case 2:
                    break;
                default:
                    puts("Keyboard don't recognize");
                    break;
            }
        }
    }

    return number;
}

谁能帮我解决这个错误吗？

Answer 1

您似乎在帖子中实现了递归。但是代码中的某些行是不需要的，并且阻碍了递归算法的潜在效率。

递归算法的本质可以用两条语句来概括:

1) Each recursive call should be on a smaller instance of the same problem, that is, a smaller subproblem.
2) The recursive calls must eventually reach a base case, which is solved without further recursion.
(from here)

以下是对原始 EnterNumber() 函数的改编，简化为仅包含上面列出的递归算法的基本要素。

• reads and tests input character (smaller instance...)
• leaves when test fails criteria (base case...)

它可以根据需要进行扩展，以包含您在原始帖子中所需的其他功能(例如更多用户输入，或通知用户输入不是数字)

void EnterNumber(char a);

int main(void)
{

    char c;
    int num;

    printf("Enter your number:");
    scanf(" %c", &c);
    //     ^ notice space preceeding format char, 
    //       comsumes newline from previous read and allows next input
    num = isdigit(c);
    EnterNumber(c);
    printf("\nHit any key to exit\n");
    getchar();
    return 0;
}

/// Simple demo of recursion:
/// caches input as long as it is a number
/// outputs cache and exits if alpha char
void EnterNumber(char a)
{
    if(isdigit(a) != 0)
    {
        printf("Enter your number:");
        scanf(" %c", &a);
        //     ^ notice space preceeding format char, 
        //       comsumes newline from previous read and allows next input
        EnterNumber(a);    
    }
    printf("%c\n", a);
}

关于 scanf() 格式字符串中的空格功能:

Whitespace character: the function will read and ignore any whitespace characters encountered before the next non-whitespace character (whitespace characters include spaces, newline and tab characters -- see isspace). A single whitespace in the format string validates any quantity of whitespace characters extracted from the stream (including none). (from here)