如果该语句为真，如何只显示一条printf语句？

Question

如果包裹重量超过50磅，我将制造一个运输计算器，则无法运输包裹。 我只想在包装重量超过50磅时才显示一个声明，但是无论如何看起来都没有。

我尝试了它作为else语句，if语句和if else语句。

main(){
    double distance, weight, weightCharges, shippingCharge, distanceCharge, unableToShip;
    printf ("Enter the weight of the package:\n");
    scanf ("%lf", &weight);
    printf ("Enter the distance your package needs to go: \n");
    scanf ("%lf", &distance);

    if (weight <= 10)
        weightCharges = weight * 3.00;
        else
            if (weight <= 50)
                weightCharges = weight * 5.00;
            else (weight > 50);
        weightCharges= 0;
    if (distance > 1000)
        distanceCharge = weightCharges + 10;
    shippingCharge = weightCharges + distanceCharge;
    unableToShip = weight > 50;

    printf ("Your total cost is: %.2lf \n", shippingCharge);
    printf ("We're unable to ship your package \n", unableToShip);

}

我希望仅当我们无法运送其包装时才会出现第二个printf，但是无论如何它都会出现。

Answer 1

您是否尝试放置一些if-else语句？

int main()
{
    double distance, weight, weightCharges, shippingCharge, distanceCharge; // no need for unableToShip;
    printf ("Enter the weight of the package:\n");
    scanf ("%lf", &weight);
    printf ("Enter the distance your package needs to go: \n");
    scanf ("%lf", &distance);

    if (weight <= 10)
        weightCharges = weight * 3.00;
        else
            if (weight <= 50)
                weightCharges = weight * 5.00;
            else (weight > 50);
        weightCharges= 0;
    if (distance > 1000)
        distanceCharge = weightCharges + 10;
    shippingCharge = weightCharges + distanceCharge;
    //unableToShip = ;

    printf ("Your total cost is: %.2lf \n", shippingCharge);
    if(weight > 50)
    printf ("We're unable to ship your package \n");

}

Answer 2

if在这里的工作方式与其他地方相同：

if (unableToShip) 
  printf ("We're unable to ship your package\n");

Answer 3

int main(){
    double distance, weight, weightCharges, shippingCharge, distanceCharge, unableToShip;
    printf ("Enter the weight of the package:\n");
    scanf ("%lf", &weight);
    printf ("Enter the distance your package needs to go: \n");
    scanf ("%lf", &distance);

    if (weight <= 20)
        weightCharges = weight * 5.00;
        else
            if (weight <= 100)
                weightCharges = weight * 10.00;
            else (weight > 100);
        weightCharges= 0;
    if (distance > 1000)
        distanceCharge = weightCharges + 20;
    shippingCharge = weightCharges + distanceCharge;
    unableToShip = weight > 100;

    printf ("Your total cost is: %.2lf \n", shippingCharge);
    printf ("We're unable to ship your package \n", unableToShip);

}

Answer 4

首先， unableToShip应该为int或bool类型（如果您使用的是最新且支持<stdbool.h>的编译器）。 double在这种情况下并不能很好地工作。

其次，即使unableToShip是布尔条件的正确类型，将其作为参数传递给printf也不会使printf有条件地工作。 如果您有格式字符串可以接受，那么它将成为格式化输出的一部分。 您需要准备的是if (unableToShip)后跟printf语句。

第三，如果要打印的字符串不包含任何格式并以新行结尾，则应使用puts而不是printf 。