为什么我的程序打印的是 0 而不是预期的值？ (C) [重复]

Question

我正在尝试为我的班级制作一个计算器程序（如您所知，尚未完全完成），但我遇到了乘法和除法部分的问题。它们都打印出 0 而不是它们的预期值，但加法和减法工作正常。有什么帮助吗？

int choice = 8;
double numberone;
double numbertwo;
    
while(choice > 7 || choice < 1){
    printf("(1) Addition \n(2) Subtraction \n(3) Multiplication \n(4) Division \n(5) Modulus (integers only) \n(6) Test if prime (integers only) \n(7) Exit \nPlease choose an operation: \n");
    scanf(" %i", &choice);
    
    if (choice != 5 || choice!= 6){
        printf("Enter the first number: ");
        scanf(" %d", &numberone);
        
        printf("Enter the second number: ");
        scanf(" %d", &numbertwo);
        
        if (choice == 1){
            double sum = numberone + numbertwo;
            printf("Sum: %d", sum);
        }
        else if (choice == 2){
            double dif = numberone - numbertwo;
            printf("Difference: %d", dif);
        }
        else if (choice == 3){
            double pro = numberone * numbertwo;
            printf("Product: %d", pro);
        }
        else if (choice == 4){
            double quo = numberone / numbertwo;
            printf("Quotient: %d", quo);
        }
    }
}
}

Answer 1

您在printf 中使用%d，它将您的结果转换为整数。请改用%lf。

// ...
        else if (choice == 3){
            double pro = numberone * numbertwo;
            printf("Product: %lf", pro);
        }
        else if (choice == 4){
            double quo = numberone / numbertwo;
            printf("Quotient: %lf", quo);
// ...

编辑： 这同样适用于您的 scanf。使用%lf 而不是%i：

// ...
       printf("Enter the first number: ");
       scanf(" %lf", &numberone);
        
       printf("Enter the second number: ");
       scanf(" %lf", &numbertwo);
// ...