3.example

Example 3.1

读入一个整数a，如果a为偶数在屏幕上输出yes。

[+]

#include <iostream>
using namespace std;

int main(){
	int a;
	
	cin >> a;
	if(a%2==0)
		cout << "yes" << endl;
	
	return 0;
}

Example 3.2

读入一个数，若这个数大于1并且小于100，则输出yes。

[+]

#include <iostream>
using namespace std;

int main(){
	int a;
	
	cin >> a;
	if((a>1)&&(a<100))
		cout << "yes" << endl;
	
	return 0;
}

Example 3.3

输入三个整数，按从大到小的顺序输出。

[+]

#include <iostream>
using namespace std;

int main(){
	int a,b,c,temp;
	
	cin >> a >> b >> c;
	if(a<b){
		temp = a;
		a = b;
		b = temp;
	}
	if(a<c){
		temp = a;
		a = c;
		c = temp;
	}
	if(b<c){
		temp = b;
		b = c;
		c = temp;
	}
	cout << a << " " << b << " " << c << endl;
	
	return 0;
}

Example 3.4

输入温度t的值，判断是否适合晨练。（25<=t<=30，则适合晨练ok，否则不适合no）

[+]

#include <iostream>
using namespace std;

int main(){
	int t;
	
	cin >> t;
	if( (t>=25) && (t<=30))
		cout << "ok!" << endl;
	else
		cout << "on!" << endl;
		
	return 0;
}

Example 3.5

输入三个数，输出其中最大的数。

[+]

#include <iostream>
using namespace std;

int main(){
	float a,b,c,maxn;
	
	cin >> a >> b >> c;
	if(a>b && a>c)
		maxn = a;
	else if ( b>a && b>c)
		maxn = b;
	else
		maxn = c;
	cout << maxn << endl;
	
	return 0;
}

[+]

#include <iostream>
using namespace std;

int main(){
	float a,b,c,maxn;
	
	cin >> a >> b >> c;
	maxn = a;
	if(b>maxn) maxn=b;
	if(c>maxn) maxn=c;
	cout << maxn << endl;
	
	return 0;
}

Example 3.6

乘坐飞机时，当乘客行李小于等于20公斤时，按每公斤1.68元收费，大于20公斤时，按每公斤1.98元收费，编程计算收费（保留2位小数）。

[+]

#include <iostream>
using namespace std;

int main(){
	float w,s;
	scanf("%f",&w);
	if(w<=20){
		s = w*1.68;
	}else{
		s = w*1.98;	
	}
	printf("%.2f\n",s);
	
	return 0;
}

Exercise 1

判断数正负，http://noi.openjudge.cn/ch0104/01/[+]

#include <iostream>
using namespace std;

int main()
{
	int n;
	cin >> n;
	string s = "positive";
	if (n ==0)	
		s = "zero";
	else if (n<0)
		s = "negative";
	cout << s << endl;
				
	return 0;
}

输出绝对值，http://noi.openjudge.cn/ch0104/02/[+]

#include <iostream>
using namespace std;

int main()
{
	double n;
	cin >> n;
	if (n<0)
		n = -n;
	printf("%.2f",n);
	
	return 0;
}

奇偶数判断，http://noi.openjudge.cn/ch0104/03/[+]

#include <iostream>
using namespace std;
//03:奇偶数判断
int main()
{
	int n;
	cin >> n;
	string s = "even";
	if (n%2==1)
		s = "odd";
	
	cout << s << endl;
	
	return 0;
}

奇偶ASCII值判断，http://noi.openjudge.cn/ch0104/04/[+]

#include <iostream>
using namespace std;
//04:奇偶ASCII值判断
int main()
{
	char c=getchar();
	string s = "NO";
	if (c%2==1)
		s = "YES";
	
	cout << s << endl;
	
	return 0;
}

整数大小比较，http://noi.openjudge.cn/ch0104/05/[+]

#include <iostream>
using namespace std;
//05:整数大小比较
int main()
{
	int x,y;
	cin >> x >> y;
	
	string s = ">";
	if (x==y)
		s = "=";
	else if (x <y)
		s = "<"; 
	
	cout << s << endl;
	
	return 0;
}

判断是否为两位数，http://noi.openjudge.cn/ch0104/06/[+]

#include <iostream>
using namespace std;
//06:判断是否为两位数
int main()
{
	int i;
	cin >> i;

	if (i>=10 && i<=99)
		i = 1;
	else
		i = 0;		
	
	cout << i << endl;
	
	return 0;
}

收集瓶盖赢大奖，http://noi.openjudge.cn/ch0104/07/[+]

#include <iostream>
using namespace std;
//07:收集瓶盖赢大奖
int main()
{
	int x,y,z;
	cin >> x >> y;

	if (x>=10 || y >= 20)
		z = 1;
	else
		z = 0;		
	
	cout << z << endl;
	
	return 0;
}

判断一个数能否同时被3和5整除，http://noi.openjudge.cn/ch0104/08/[+]

#include <iostream>
using namespace std;
//08:判断一个数能否同时被3和5整除
int main()
{
	int n;
	cin >> n;
	string s = "NO";
	if (n % 3==0 && n % 5==0)
		s = "YES";
	
	cout << s << endl;
	
	return 0;
}

判断能否被3，5，7整除，http://noi.openjudge.cn/ch0104/09/[+]

#include <iostream>
using namespace std;

int main(){
	int a; //装整数的筐 
	
	cin >> a ;
	if(a%3==0 && a%5==0 && a%7==0){
		cout << 3 << " " << 5 << " " << 7 << endl;
	}else if(a%3==0 && a%5==0){
		cout << 3 << " " << 5 << endl;
	}else if(a%5==0 && a%7==0){
		cout << 5 << " " << 7 << endl;
	}else if(a%3==0 && a%7==0){
		cout << 3 << " " << 7 << endl;
	}else if(a%3==0){
		cout << 3 << endl;
	}else if(a%5==0){
		cout << 5 << endl;
	}else if(a%7==0){
		cout << 7 << endl;
	}else{
		cout << "n" << endl;
	}
	
	return 0;
}

有一门课不及格的学生，http://noi.openjudge.cn/ch0104/10/[+]

#include <iostream>
using namespace std;
//10:有一门课不及格的学生
int main()
{
	int c1,c2;
	cin >> c1 >> c2;
	string s = "0";

	if ((c1<60 && c2>=60 )|| (c1>=60 && c2 <60))
		s = "1";
	
	cout << s << endl;
	
	return 0;
}

Example 3.7

根据从键盘上输入的表示星期几的数字，对应输出它的英文名称。

[+]

#include <iostream>
using namespace std;

int main(){
	int weekday;
	cin >> weekday;
	switch(weekday){
		case 1: cout << "Monday" << endl; break;
		case 2: cout << "Tuesday" << endl; break;
		case 3: cout << "Wednessday" << endl; break;
		case 4: cout << "Thursday" << endl; break;
		case 5: cout << "Friday" << endl; break;
		case 6: cout << "Saturday" << endl; break;
		case 7: cout << "Sunday" << endl; break;
		default: cout << "Input error!" << endl; break;
	}
	
	return 0;
}

Example 3.8

一个最简单的计算器支持+，-，*，/四种运算。输入只有一行：两个参加运算的数和一个操作符（+，-，*，/)。输出运算表达式的结果。考虑下面两种情况：

如果出现除数为0的情况，则输出：Divided by zero!
如果出现无效的操作（即不为+，-，*，/之一），则输出：Invalid operator！

输入样例：

34 56 +

输出样例：

样例程序：

[+]

#include <iostream>
using namespace std;

int main(){
	float num1,num2;
	char opt;
	
	cin >> num1 >> num2 >> opt;
	switch(opt){
		case '+': cout << num1+num2 << endl; break;
		case '-': cout << num1-num2 << endl; break;
		case '*': cout << num1*num2 << endl; break;
		case '/':
			if(num2!=0)
				cout << num1/num2 << endl;
			else
				cout << "Divided by zero!" << endl;
			break;
		default: cout << "Invalid operator!" << endl;
	}
		
	return 0;
}

Example 3.9

期末来临了，班长小Q决定将剩余的班费x元钱，用于购买若干支钢笔奖励给一些学习好、表现好的同学。
已知商店里有三种钢笔，它们的单价分别为6元，5元和4元。
小Q想买尽量多的笔（鼓励尽量多的同学），同时他又不想有剩余的钱。

请你编一个程序，帮小Q制定出一种买笔的方案。

[+]

#include <iostream>
using namespace std;

int main(){
	int a,b,c,x,y;
		
	cin >> x;
	
	c=x/4; 	//能买4元的多少只 
	y=x%4;	//都买4元的剩余多少钱 
	
	switch(y){
		case 0: //都买4元的正好 
			a=0; 
			b=0; 
			break;	 
		case 1:	//买4元的剩1元，少买一个4元的多买一个5元的 
			a=0; 
			b=1; 
			c--; 
			break;
		case 2: //买4元的剩2元，少买一个4元的多买一个6元的 
			a=1; 
			b=0; 
			c--; 
			break;
		case 3:	//买4元的剩3元，少买两个4元的，多买一个5元的和一个6元的 
			a=1; 
			b=1; 
			c-=2; 
			break;
	}

	cout << a << " " << b << " " << c << endl;
			
	return 0;
}

Exercise 2

晶晶赴约会，http://noi.openjudge.cn/ch0104/11/[+]

#include <iostream>
using namespace std;
//11:晶晶赴约会
int main()
{
	int d;
	cin >> d;
	string s = "YES";

	if (d==1 || d==3 || d == 5 )
		s = "NO";
	
	cout << s << endl;
	
	return 0;
}

骑车与走路，http://noi.openjudge.cn/ch0104/12/[+]

#include <iostream>
using namespace std;
//12:骑车与走路
int main()
{
	double m;
	cin >> m;
	string s = "All";
	
	double bikeTime = m / 3.0 + 50;
	double walkTime = m / 1.2;
	
	if ( bikeTime < walkTime )
		s = "Bike";
	else if (bikeTime > walkTime)
		s = "Walk";
		
	cout << s << endl;
	
	return 0;
}

分段函数，http://noi.openjudge.cn/ch0104/13/[+]

#include <iostream>
using namespace std;
//13:分段函数
int main()
{
	double n,f=0;
	cin >> n;
	
	if ( n>=0 && n < 5 )
		f = -n + 2.5;
	else if (n>=5 && n<10)
		f = 2 -1.5*(n-3)*(n-3);
	else if (n>=10 && n<20)
		f = n / 2 - 1.5;
		
	printf("%.3f",f);
	
	return 0;
}

计算邮资，http://noi.openjudge.cn/ch0104/14/[+]

#include <iostream>
#include <cmath>
using namespace std;
//14:计算邮资
int main()
{
	double w;
	char c;
	int f;
	cin >> w >> c;
	
	if (w <= 1000)
		f = 8;
	else
		f = ceil((w-1000)/500)*4 + 8;
		
	if (c=='y')
		f = f + 5;
		
	printf("%d",f);
	
	return 0;
}

最大数输出，http://noi.openjudge.cn/ch0104/15/[+]

#include <iostream>
using namespace std;

int main(){
	int a,b,c;
	cin >> a >> b >> c;
	if(a>b && b>c){
		cout << a << endl;
	}else if(b>c){
		cout << b << endl;
	}else{
		cout << c << endl; 
	}
	
	return 0;
}

三角形判断，http://noi.openjudge.cn/ch0104/16/[+]

#include <iostream>
using namespace std;
//16:三角形判断
int main()
{
	int x,y,z;
	cin >> x >> y >>z;
	string s = "yes";
	if (x + y <= z)
		s = "no";
	else if(x + z <= y)
		s = "no";
	else if(y + z <= x)				
		s = "no";
						
	cout << s << endl;
	
	return 0;
}

判断闰年，http://noi.openjudge.cn/ch0104/17/[+]

#include <iostream>
using namespace std;
//17:判断闰年
int main()
{
	int y;
	cin >> y;
	
	string s = "N";
	
	if (y % 4 ==0 && !(y % 100==0 && y % 400 !=0) && !(y%3200==0))
		s = "Y";
						
	cout << s << endl;
	
	return 0;
}

点和正方形的关系，http://noi.openjudge.cn/ch0104/18/[+]

#include <iostream>
using namespace std;
//18:点和正方形的关系
int main()
{
	int x,y;
	cin >>x >> y;
	
	string s = "no";
	
	if (x<=1 && x>=-1 && y <=1 && y>=-1)
		s = "yes";
						
	cout << s << endl;
	
	return 0;
}

简单计算器，http://noi.openjudge.cn/ch0104/19/[+]

#include <iostream>
using namespace std;
//18:点和正方形的关系
int main()
{
	int x,y;
	char c;
	int result = 0;
	
	cin >>x >> y >> c;
	
	string s = "";
	
	switch(c)
	{
		case '+':
			result = x + y;
			break;
		case '-':
			result = x - y;
			break;
		case '*':
			result = x * y;
			break;
		case '/':
			if (y==0)
				s = "Divided by zero!";
			else
				result = x / y;
			break;
		default:
			s = "Invalid operator!";		
	}	
	
	if (s=="")
		cout << result << endl;
	else
		cout << s << endl;
	
	return 0;
}

求一元二次方程的根，http://noi.openjudge.cn/ch0104/20/[+]

#include <iostream>
#include <cmath>
using namespace std;

int main()
{
	double a,b,c;
	cin >> a >> b >> c;
	
	double b2 = b * b;
	double dt = 4 * a * c;
	double a2 = 2 * a;
	
	if (b2 < dt)
	{
		double r = -b / a2;
		if (b==0){
			r = 0;
		}
		double v = sqrt(dt-b2)/a2;
		printf("x1=%.5f+%.5fi;x2=%.5f-%.5fi",r,v,r,v);
		
	}else{
		double x1 = (-b + sqrt(b2-dt))/a2;
		double x2 = (-b - sqrt(b2-dt))/a2;
		if (b2>dt)
		{
			printf("x1=%.5f;x2=%.5f",x1,x2);
		}else{
			printf("x1=x2=%.5f",x1);
		}
	}

	return 0;		
}

苹果和虫子2，http://noi.openjudge.cn/ch0104/21/[+]

#include <iostream>
using namespace std;

int main(){
	int n;  //苹果数量 
	int x;  //虫子吃一个苹果花的时间 
	int y; 	//虫子吃了多少时间的苹果
	
	cin >> n>> x >>y;  //分别输入苹果个数，虫子吃一个苹果的时间，虫子吃了多长时间的苹果 
	
	if(n>0){ 	//如果箱子里有苹果 
		if(x>0){
			if(y>0){
				int m = y/x; //计算吃了几个整苹果
				if(y%x!=0)
					m = m + 1;
					if(n-m>0)
						cout << n-m << endl;
							else
								cout << "0" << endl;
			}else{
				cout << n << endl;
			}
		}else{
			cout << n << endl;
		}
	}else{ 		//否则，箱子里没有苹果 
		cout << "0" << endl;
	}
	
	
	return 0;
}

参考文献

董永建，信息学奥数一本通（C++）第五版。
http://noi.openjudge.cn

辽师张大为@https://daweizh.github.io/csp/