c:如何用信号通知输入结束 [英] c : How to signal end of input

问题描述

在这个提示用户输入多项式的简单程序中，

in this simple program that prompts users to input a polynomial,

我将int 999用作代表输入结束的值.

I used int 999 as a value that represents end of input.

但是，这不是一个好的设计，因为用户将无法输入系数为999的多项式节点.

However, this is not a good design because users will not be able to input a polynomial node with a coeff of 999.

是否存在可以唯一表示输入结束的替代键?

Is there an alternative key that can be unique to represent end of input?

相关代码:

int coeff;
int expon;
int i = 1;

printf("\nInput for polyNode %d  (999 for exit):",i);
printf("\n\tInput coeff : ");
scanf("%d",&coeff);

while(coeff != 999)
{
    printf("\tInput expon : ");
    scanf("%d",&expon);
    insertBack(&polynomial, &polynomialRear, coeff, expon);

    i++;
    printf("\nInput for polyNode %d  (EOF for exit):",i);
    printf("\n\tInput coeff : ");
    scanf("%d",&coeff);
}

printPoly(polynomial);
printf("\n");

推荐答案

您可以检查scanf的返回值.如果扫描成功，在这种情况下，将为扫描的一项返回1.如果扫描不成功，它将返回0或EOF.输入任何非整数值(字母...)将结束while ( 1)循环.
然后在一个while循环中使用getchar()清除输入流.

You can check the return of scanf. If the scan is successful it will, in this case, return 1 for one item scanned. If the scan is unsuccessful, it will return either 0 or EOF. Input of any non-integer value (letters...) will end the while ( 1) loop.
Then clear the input stream with getchar() in a while loop.

int coeff;
int expon;
int i = 1;

while(1)
{
    printf("\nInput for polyNode %d :",i);
    printf("\n\tInput coeff : ");
    if ( ( scanf("%d",&coeff)) != 1) {
        break;
    }

    printf("\tInput expon : ");
    if ( ( scanf("%d",&expon)) != 1) {
        break;
    }

    insertBack(&polynomial, &polynomialRear, coeff, expon);

    i++;
}
while ( ( i = getchar ()) != '\n' && i != EOF) ;//clear input stream

printPoly(polynomial);
printf("\n");

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