求大神看看还有什么功能可以再添进去

#include<iostream>
#include<stdio.h>
#include<math.h>
#include<stdlib.h>
#define pi 3.14
using namespace std;
void _1();
void _2();
void _3();
void _4();
void _5();
void _6();
int main()
{
   cout<<"*******************************************"<<endl;
   cout<<"*        图形面积与体积计算小程序         *"<<endl;
   cout<<"*          以下是各种图形序号:            *"<<endl;
   cout<<"*          1.三      角     形            *"<<endl;
   cout<<"*          2.圆             形            *"<<endl;
   cout<<"*          3.平  行  四  边 形            *"<<endl;
   cout<<"*          4.梯             形            *"<<endl;
   cout<<"*          5.圆             环            *"<<endl;
   cout<<"*******************************************"<<endl;
    char yn;
    int i;
    cout<<"请输入您所需求的图形号码："<<endl;
    cin>>i;
    switch(i)
    {
        case 1:
            cout<<"您所求的图形为三角形,请确认是否正确"<<endl;
            cout<<"正确请输入'y'"<<endl;
            cin>>yn;
            if(yn=='y')
             _1();
            else
            main();
            break;
        case 2:
            cout<<"您所求的图形为圆形，请确认是否正确"<<endl;
            cin>>yn;
            if(yn=='y')
              _2();
            else
              main();
            break;
        case 3:
            cout<<"您所求的图形为平行四边形，请确认是否正确"<<endl;
            cin>>yn;
            if(yn=='y')
              _3();
            else
              main();
            break;   
        case 4:
            cout<<"您所求的图形为梯形，请确认是否正确"<<endl;
            cin>>yn;
            if(yn=='y')
              _4();
            else
              main();
            break;   
        case 5:
            cout<<"您所求的图形为圆环，请确认是否正确"<<endl;
            cin>>yn;
            if(yn=='y')
              _5();
            else
              main();
            break;   
        //case 6:
            
    //    case 2:
        default:cout<<"输入非法"<<endl;
    }
}
void xuanze()
{
   
    int i;
    cin>>i;
    switch(i)
       {
        case 1:_1();
        break;
        case 2:_2();
        break;
        case 3:_3();
        break;
        case 4:_4();
        break;
        case 5:_5();
        break;
        case 6:_6();
        break;
        default:
        cout<<"请重新启动"<<endl;
       }
        //return 0;     
}
void _1()
{
  float a,b,c,s,area;
  char j;
  cout<<"请输入三角形的三条边长："<<endl;
  cin>>a>>b>>c;
  s=(a+b+c)/2;
  area=sqrt(s*(s-a)*(s-b)*(s-c));
  cout<<"三角形的半周长s="<<s<<endl;
  cout<<"三角形的面积area="<<area<<endl;
  cout<<"是否继续计算？"<<endl;
  cin>>j;
  if(j=='y')
  main();
  else
  _6();
}
void _2()
{
    float r,area;
    char j;
    cout<<"请输入圆形的半径："<<endl;
    cin>>r;
    area=r*r*pi;
    cout<<"圆形的面积area="<<area<<endl;
    cout<<"是否继续计算？"<<endl;
  cin>>j;
  if(j=='y')
  main();
  else
  _6();
}
void _3()
{
    float a,h,area;
    char j;
    cout<<"请输入平行四边形的高和底边长："<<endl;
    cin>>a>>h;
    area=a*h;
    cout<<"平行四边形的面积area="<<area<<endl;
    cout<<"是否继续计算？"<<endl;
  cin>>j;
  if(j=='y')
  main();
  else
  _6();
}
void _4()
{
    float a,b,h,area;
    char j;
    cout<<"请输入梯形的上底，下底和高："<<endl;
    cin>>a>>b>>h;
    area=(a+b)*h/2;
    cout<<"梯形的面积area="<<area<<endl;
    cout<<"是否继续计算？"<<endl;
  cin>>j;
  if(j=='y')
  main();
  else
  _6();
    }
void _5()
{
    float R,r,area;
    char j;
    cout<<"R为外圆半径，r为内圆半径"<<endl;
    cin>>R>>r;
    area=pi*(R*R-r*r);
    cout<<"圆环面积area="<<area<<endl;
    cout<<"是否继续计算？"<<endl;
  cin>>j;
  if(j=='y')
  main();
  else
  _6();
}
void _6()
{
    exit(1);
}

还可以加上 矩形 长方形 的面积求解，三角形是分种类的，可以区分一下，还有体积求解你好没有做啊？可以加上去，我觉得这种小程序还是很有意思的。

不会！

void xuanze()怎么没有被调用？