getchar(),gets()

最重要的区别是gets读一行，getchar()()读一个字符。

先看原型：
char() * gets(char() * ptr);
int getchar(void);

作用是：

gets()用于从标准输入流stdin读入一个整行（以'\n'或EOF）结束，写入ptr指向的字符数组，并返回这个指针；出错或遇到文件结束时则返回NULL。行末的'\n'从流中取出，但不写入数组。gets()不检查被写入的数组大小。

getchar()用于从标准输入流stdin读入一个字符，并返回这个字符。如果读到文件结尾，则返回EOF。注意到EOF不能用char类型表示，所以getchar()函数返回的是一个int型的数。使用时也应该注意这一点。

#include<stdio.h>
#include<stdlib.h>
int main()
{system("color f5");printf("     *\n    **\n     ***\n");system("pause");return 0;
}

#include<iostream>
#include<math.h>
using namespace std;class Shape
{
public:virtual double Area() const = 0;virtual double Perim() const = 0;virtual void Show(){cout << "Area is:" << Area() << endl;cout << "Perim is:" << Perim() << endl;}
};class Rectangle:public Shape
{
private:double Length;double Width;
public:Rectangle(double Length = 0,double Width = 0){this->Length = Length;this->Width = Width;}~Rectangle(){}double Area() const{return Length*Width;}double Perim() const{return 2*(Length+Width);}/*void Show( ){cout << "Area is:" << Area() << endl;cout << "Perim is:" << Perim() << endl;}*/
};const double PI = 3.14159;
class Circle:public Shape
{
private:double Radius;
public:Circle(double Radius = 0){this->Radius = Radius;}~Circle(){}double Area()const{return PI*Radius*Radius;}double Perim() const{return 2*PI*Radius;}/*void show(){cout << "Area is:" << Area() << endl;cout << "Perim is:" << Perim() << endl;}*/
};class Triangle:public Shape
{
private:double A,B,C;
public:Triangle(double A = 0,double B = 0,double C = 0){this->A = A;this->B = B;this->C = C;}~Triangle(){}double Area() const{double P;P = (A +B + C)/2;return sqrt(P*(P-A)*(P-B)*(P-C));}double Perim() const{return(A+B+C);}/*void show(){cout << "Area is:" << Area() << endl;cout << "Perim is:" << Perim() << endl;}*/};void main()
{double Length,Width,Radius,A,B,C;cout << "Rectangle :" << endl;
loopa:cout << "请输入矩形的长河宽(Length,Width):" << endl;cin >> Length >> Width;if(Length <= 0||Width <= 0){cout << "输入的长度不能构成一个矩形!请重新输入!" <<endl;goto loopa;}else{Rectangle Rect(Length,Width);Rect.Show();cout << "Circle: "<<endl;}loopb:cout << "请输入圆形的半径(Radius): " << endl;cin >> Radius;if(Radius <= 0){cout << "输入的半径不能构成一个圆!请重新输入!" << endl;goto loopb;}else{Circle Cir(Radius);Cir.Show();cout << "Triangle:" << endl;}loopc:cout << "请输入三角形的三边(A,B,C): "<< endl;cin >> A >> B >> C;if(A <= 0||B <= 0||C <= 0 ||(A+B) <= C || (A + C) <= B||(B + C) <= A){cout << "输入的三边值不能构成一个三角形!请重新输入!" << endl;goto loopc;}else{Triangle Tri(A,B,C);Tri.Show();}
}