C primer plus (第六版）第六章 编程练习第8, 9题

题目：

8．编写一个程序，要求用户输入两个浮点数，并打印两数之差除以两数乘积的结果。在用户输入非数字之前，程序应循环处理用户输入的每对值。

#include 
int main()
{
    double num1, num2;
    double num_diff, num_multiply;
    int temp;

    printf("Please entry two float numbers:\n");
    temp = scanf("%lf %lf",&num1, &num2);
    
    while (temp == 2)
    {
        num_diff = num1 - num2;
        num_multiply = num1 * num2;

        printf("the result is: %lf\n",num_diff/num_multiply);
        printf("Please entry two float numbers again(q to quite):\n");
        temp = scanf("%lf %lf",&num1, &num2);        
    }
    printf("Thanks to use this program\n");

    return 0;
}

9．修改练习8，使用一个函数返回计算的结果。

#include 
double calculate(double num1, double num2);
int main()
{
    double num1, num2, result2;
    int temp;

    printf("Please entry two float numbers:\n");
    temp = scanf("%lf %lf",&num1, &num2);
    
    while (temp == 2)
    {
        result2 = calculate(num1, num2);
        printf("the result is: %lf\n",result2);
        printf("Please entry two float numbers again(q to quite):\n");
        temp = scanf("%lf %lf",&num1, &num2);        
    }
    printf("Thanks to use this program\n");

    return 0;
}

double calculate(double num1, double num2)
{
    double result1;
    result1 = (num1 - num2) / (num1 * num2);

    return result1;
}