C 程序输出不正确？

Question

我正在编写一个 C 程序，它计算平均成绩并告诉你是否通过。用户可以选择任意次数的尝试，并且他们将获得所有尝试的最终平均值。这是我的代码:

#include <stdio.h>

int main(void)
{
    int num1;
    double num2, num3, average, average_1;

    printf("Enter number of attempts: ");
    scanf("%d", &num1);

    while (num1 > 0) {
        printf("Enter your mark for subject one: ");
        scanf("%lf", &num2);

        printf("Enter your mark for subject two: ");
        scanf("%lf", &num3);

        if (num2 < 50 || num3 < 50) {
            printf("You have failed \n");
        } else {
            printf("You have passed \n");
        }

        num1--;
    }

    average = num1 * num2 * num3;
    average_1 = average / 100;

    printf("Average for all %d attempts is %.2f \n", num1, average_1);
}

此代码的问题在于，最终输出(即 printf 的最后一行)给出的尝试次数为 0，平均次数为 0。这是确切的输出:

Enter number of attempts: 2Enter your mark for subject one: 49Enter your mark for subject two: 96You have failedEnter your mark for subject one: 22Enter your mark for subject two: 100You have failedAverage for all 0 attempts is 0.00

Answer 1

您正在对变量 num1 进行减一操作。因此，当你完成循环时，你将得到 num1 = 0。

我建议你用“for”而不是“while”。像这样:

#include <stdio.h>

int main(void) {

int num1, i;
double num2,num3,average,average_1;

printf("Enter number of attempts: ");
scanf("%d", &num1);

for(i = num1; i > 0; i--) {

        printf("Enter your mark for subject one: ");
        scanf("%lf", &num2);

        printf("Enter your mark for subject two: ");
        scanf("%lf", &num3);

        if (num2 < 50 || num3 < 50) {

                printf("You have failed \n");
        }
        else {
                printf("You have passed \n");
        }
}

average = num1*num2*num3;
average_1 = average / 100;
printf("Average for all %d attempts is %.2f \n", num1, average_1);
}