以下是一个简单的求圆面积和圆周的程序，具体的要求是：
1. 按照输入的半径来计算面积和圆周；
2. 输入的半径必须大于0，否侧，系统会要求重新输入有效半径值；
3. 当输入-1为半径值的时候，系统结束计算。并且结束之后统计输入有效半径次数和一共输入的有效半径的总和。

现在遇到的难题是：关于计算和统计都没有问题，只是在输入-1来结束程序的时候，程序总是要先计算-1为半径的圆周和面积，再进行总体的统计。

怎样才能让系统跳过计算半径为-1的圆周和面积？

我刚开始学C语言不到2周，实在是没法解决这个问题。请高手帮忙解惑。先谢过了。

#include "stdafx.h"
#include "stdio.h"
#define PI 3.14159265
int _tmain(int argc, _TCHAR* argv[])
{
    double radius=0.0;
    double circumference =0.0;
    double area = 0.0;
    int calculation_counted = -1; // adjustment because of the circule which has the radius=-1 (to end) will be counted
    double sum_radiuses= 1.0; // adjustment because of the radius=-1 will be entered to end

    while (radius != -1)
    {   
        printf ("Please enter a radius value (-1 to end): ");
        scanf_s ("%lf", &radius);
               
        while ((radius<-1) || (-1 < radius && radius< 0))// radius must be bigger than 0
        {
        printf ("The radius must >=0, enterd a valid radius (or -1 to end): ");
        scanf_s ("%lf", &radius);
        }
        
        circumference = 2*PI*radius;// circumference equation
        area = PI*radius*radius; // area equation

        calculation_counted = calculation_counted + 1;
        sum_radiuses = sum_radiuses + radius;
        
        printf ("The ciucumference is %lf \n", circumference); // %lf, %#.#f.... depends on the requirement
        printf ("The area is %lf\n\n", area);     
    }
   
    printf ("%d valid radiuses have been counted,\n ", calculation_counted);
    printf ("The sum of valid radiuses is %5.2f\n ", sum_radiuses);
    printf ("\n\n");

    return 0;
}

你那两个循环是什么意思？

if （radius != -1）
{
        circumference = 2*PI*radius;// circumference equation
        area = PI*radius*radius; // area equation
        calculation_counted = calculation_counted + 1;
        sum_radiuses = sum_radiuses + radius;
        printf ("The ciucumference is %lf \n", circumference); // %lf, %#.#f.... depends on the requirement
        printf ("The area is %lf\n\n", area);     
}

[ 本帖最后由 yyqd2013 于 2013-5-12 12:00 编辑 ]

或者：
    while (radius != -1)
    {   
        printf ("Please enter a radius value (-1 to end): ");
        scanf_s ("%lf", &radius);
               
        while ((radius<-1) || (-1 < radius && radius< 0))// radius must be bigger than 0
        {
        printf ("The radius must >=0, enterd a valid radius (or -1 to end): ");
        scanf_s ("%lf", &radius);
        }
        
        if （-1 == radius）
            continue；
        circumference = 2*PI*radius;// circumference equation
        area = PI*radius*radius; // area equation

        calculation_counted = calculation_counted + 1;
        sum_radiuses = sum_radiuses + radius;
        
        printf ("The ciucumference is %lf \n", circumference); // %lf, %#.#f.... depends on the requirement
        printf ("The area is %lf\n\n", area);     
    }

你是说那两个 while{}?

第一个是 只要radius不等于-1，就一直可以输入radius值。
第二个是 如果发现radius小于零并不等于-1，就要求输入大于零的有效radius值。

这样可以让程序不计算radius=-1的情况。

但是，最后的统计数值出现问题。一直改不好。

你记住自己的思路，进入单步调试模式，输入-1，一步一步看着指令指针是怎么流经那些代码的，看过后自然知道是怎么回事。

没看清楚。你这逻辑变复杂了。建议改为：
int calculation_counted = 0；
double sum_radiuses= 0;

用if替代while，不能循环。。。

怎样进入单步调试模式？

不好意思，我是刚刚开始学。