c - 这段代码有问题吗？有时我会得到正确答案，有时会得到一个非常大的数字

Question

有时我会得到正确的答案，比如当我输入 87 和 3 时，它会返回 261，但是当我退出程序并重新运行时它有时会返回 45481185383493847891312640.000000` 或其他一些疯狂的数字。

#include <stdio.h>

int main() {
    float pts = 0;
    float avg;
    float grade;
    float total;
    int f = 1;

    while (f == 1) {
        printf("Choose a Course Grade, and the amount of points that the course is worth: \n"
               "Enter -1 at the beginning if you want to exit\n");
        scanf("%f %f", &grade, &avg);
        if (grade == -1) {
            break;
        }
        pts += avg;
        total += (avg * grade);
        printf("%f\n", total);
    }
    printf("%f\n", (total / pts));
}

Answer 1

程序有未定义的行为，因为局部变量 total 未初始化。

将其初始化为 0 并测试 scanf() 的返回值以避免未定义的行为，这解释了您的观察结果。

这是更正后的版本:

#include <stdio.h>

int main() {
    float pts = 0.0;
    float total = 0.0;
    float avg;
    float grade;

    for (;;) {
        printf("Enter a Course Grade or -1 to exit: ");
        if (scanf("%f", &grade) != 1 || grade == -1)
            break;
        printf("Enter a the amount of points that the course is worth: ");
        if (scanf("%f", &avg) != 1)
            break
        pts += avg;
        total += avg * grade;
        printf("%f\n", total);
    }
    printf("%f\n", total / pts);
    return 0;
}