函数入门

1.用函数实现pow功能（不含形参）

#include <stdio.h>
#include <stdlib.h>

double power();

int main()
{
    double result = power();
    printf("结果是：%.2lf\n", result);
    return 0;
}

double power()
{
    double num1;
    int num2;
    int i;
    double result;
    printf("请输入底数：");
    scanf("%lf", &num1);
    printf("\n请输入指数：");
    scanf("%d", &num2);
    result = 1;
    for (i = 0; i < num2; i++)
    {
        result = result * num1;
    }
    return result;
}

2.简单面积的计算（含形参）

#include <stdio.h>
#include <stdlib.h>
#include <math.h>

double Area(double,double,double,int);
int validata();
int main()
{
    double radius,length,highth;
    int i;
    printf("请选择要计算的图形面积：\n1.圆形\n2.长方形\n3.三角形\n");
    scanf("%d",&i);
    switch(i)
    {
    case 1:
        printf("请输入圆的半径：");
         do
        {
            scanf("%lf",&radius);
            if(!validata(radius))
            {
                printf("您输入的数字不规范，请重新输入:");
            }
        }while(!validata(radius));
        printf("\n圆的面积为：%.2lf",Area(radius,0,0,1));
        break;
    case 2:
        printf("请输入长方形的长、宽：");
        do
        {
            scanf("%lf%lf",&length,&highth);
            if(!validata(length)||!validata(highth))
            {
                printf("您输入的数字不规范，请重新输入:");
            }
        }while(!validata(length)||!validata(highth));
        printf("\n长方形的面积为：%.2lf",Area(0,length,highth,2));
        break;
    case 3:
        printf("请输入圆的半径：");
         do
        {
            scanf("%lf%lf",&length,&highth);
            if(!validata(length)||!validata(highth))
            {
                printf("您输入的数字不规范，请重新输入:");
            }
        }while(!validata(length)||!validata(highth));
        printf("\n三角形的面积为：%.2lf",Area(0,length,highth,3));
        break;
    default:
        printf("请输入正确的数字形式：");
    }

    return 0;
}
double Area(double radius,double length,double highth,int i)
{
    double s;
    switch(i)
    {
    case 1:
        s=3.14*pow(radius,2);
        return s;
        break;
    case 2:
        s=length*highth;
        return s;
        break;
    case 3:
        s=length*highth/2;
        return s;
        break;
    }

    return 0;
}
int validata(double num)
{
    return num>0?1:0;
}