为什么输出0.000000？

Question

有人可以解释为什么这两个变量"area"和"peri"输出0.000000？

int main()
{

    double length, width, peri = (length*2) + (width*2), area = length*width;

    printf("Enter the length of the rectangle in centimeters: ");
    scanf("%lf", &length);
    printf("\nEnter the width of the rectangle in centimeters: ");
    scanf("%lf", &width);

    printf("The perimeter of the rectangle is %lf cm.\nThe area of the rectangle is %lf cm.", circ, area);


    return 0;
}

Answer 1

Aton,看起来如果要为变量赋一个表达式,并认为每次表达式的变量发生变化时都会计算表达式.

这在excel中是如此,但在C.

在C中,您指定将在程序流/序列通过代码时执行的计算.所以在C中你会写:

int main()
{
        double length, width, peri, area;

    printf("Enter the length of the rectangle in centimeters: ");
    scanf("%lf", &length);
    printf("\nEnter the width of the rectangle in centimeters: ");
    scanf("%lf", &width);
    peri = (length*2) + (width*2);  // <== perform calculations only now
    area = length*width;
    printf("The perimeter of the rectangle is %lf cm.\nThe area of the rectangle is %lf cm.", peri, area);

    return 0;
}