c++ switch和case的用法

#include "pch.h"
#include<iostream>
using namespace std;
const float PI = 3.1415926;
int    main() {
    int iType;
    float readius, a, b;
    while (true){
        cout << "图形的类型为？(1-圆形 2-长方形 3-正方形)";
        cin >> iType;
        switch (iType) {
        case :
            cout << "请输入圆形的直径";
            cin >> readius;
            cout << "圆的面积为" << readius * PI << "平方厘米" << endl;
            break;
        case :
            cout << "矩形的长为:";
            cin >>a;
            cout << "矩形的宽位";
            cin >> b;
            cout << "矩形的面积为:" << a * b << "平方厘米" << endl;
            break;
        case :
            cout << "请输入正方形的边长";
            cin >> a;
            cout << "正方形面积为" << a * a << "平方厘米" << endl;
        }
    }
}