c - 如何在没有 Goto 语句的情况下返回程序的开头

Question

#include <stdio.h>
#include <math.h>

long factcalc(int num1);

int main(void) 
{
    int num1;
    long factorial;
    int d;
    int out;

    printf("Please enter a number that is greater than 0");
    scanf_s("%d", &num1);

    if (num1 < 0) {
        printf("Error, number has to be greater than 0");
    } else if (num1 == 0) {
        printf("\nThe answer is 1");
    } else {
        factorial = factcalc(num1);
        printf("\nThe factorial of your number is\t %ld", factorial);
    }

    return 0;
}

long factcalc(int num1) 
{
    int factorial = 1;
    int c;

    for (c = 1; c <= num1; c++)
    factorial = factorial * c;

    return factorial;
}

我想知道，如何让程序不断询问用户输入，直到用户输入“-1”？因此，即使在计算出一个数字的阶乘之后，它也会继续要求更多数字，直到用户输入 -1 为止，当它显示错误消息等时也是如此。提前致谢。

Answer 1

可以通过引入无限循环轻松实现。

#include <stdio.h>
#include <math.h>

#ifndef _MSC_VER
#define scanf_s scanf
#endif

long factcalc(int num1);

int main(void)
{
    int num1;
    long factorial;
    int d;
    int out;

    for (;;) {
        printf("Please enter a number that is greater than 0");
        scanf_s("%d", &num1);
        if (num1 == -1) {

            break;
        }

        else if (num1 < 0) {

            printf("Error, number has to be greater than 0");
        }

        else if (num1 == 0) {

            printf("\nThe answer is 1");
        }

        else {

            factorial = factcalc(num1);
            printf("\nThe factorial of your number is\t %ld", factorial);
        }
    }

    return 0;
}

long factcalc(int num1) {

    int factorial = 1;
    int c;

    for (c = 1; c <= num1; c++)
        factorial = factorial * c;

    return factorial;
}