分支结构（洛谷——入门顺序2）

苹果和虫子

#include <iostream>
using namespace std;
int main()
{
	int m, t, s;
	cin >> m >> t >> s;

	if (t == 0) {
		cout << "0" << endl;
		return 0;
	}

	int l;

	if (s % t == 0)
		l = m - s / t;
	else l = m - s / t - 1;

	cout << l << endl;

	return 0;
}

注意点：

        1，被除数有可能是0（即t==0的时候），需要额外考虑

        2，有可能在限定时间内已经吃完了，这时候就应该输出0

数的性质

#include <iostream>
#include <cstdio>
using namespace std;
int main()
{
	int x;
	cin >> x;
	int a = 0, b = 0, c = 0, d = 0;
	if (x % 2 == 0 && x > 4 && x <= 12) a = 1;
	if (x % 2 == 0 || (x > 4 && x <= 12)) b = 1;
	if ((x % 2 == 0 && (x < 4 || x>12)) || (x % 2 != 0 && x > 4 && x <= 12)) c = 1;
	if (x % 2 != 0 && (x < 4 || x>12)) d = 1;
	cout << a << " " << b << " " << c << " " << d << endl;


	return 0;
}

闰年判断

#include <iostream>
#include <cstdio>
using namespace std;
int main()
{
	int y;
	cin >> y;
	if (y % 4 == 0 && y % 100 != 0)cout << "1" << endl;
	else if (y % 100 == 0 && y % 400 != 0)cout << "0" << endl;
	else if (y % 400 == 0)cout << "1" << endl;
	else cout << "0" << endl;


	return 0;
}

苹果

#include <iostream>
#include <cstdio>
using namespace std;
int main()
{
	int n;
	cin >> n;
	if (n == 1)cout << "Today, I ate 1 apple." << endl;
	else if (n == 0)cout << "Today, I ate 0 apple." << endl;
	else cout << "Today, I ate " << n << " apples." << endl;


	return 0;
}

洛谷团队系统

#include <iostream>
#include <cstdio>
using namespace std;
int main()
{
	int n;
	cin >> n;
	int Local = n * 5;
	int Luogu = 11 + n * 3;
	if (Local > Luogu)cout << "Luogu" << endl;
	else cout << "Local" << endl;


	return 0;
}

肥胖问题

#include <iostream>
#include <cstdio>
#include <iomanip>
using namespace std;
int main()
{
	float m, h;
	cin >> m >> h;
	if (m / (h * h) < 18.5)cout << "Underweight";
	else if (m / (h * h) >= 18.5 && m / (h * h) < 24)cout << "Normal";
	else if (m / (h * h) >= 24)cout << setprecision(6) << m / (h * h) << endl << "Overweight";

	return 0;
}

有效数字：setprecision

三位数排序

#include <iostream>
#include <cstdio>
#include <iomanip>
using namespace std;
int main()
{
	int a, b, c;
	cin >> a >> b >> c;
	if (a > b)swap(a, b);
	if (b > c)swap(b, c);
	if (a > b)swap(a, b);
	cout << a << " " << b << " " << c << endl;



	return 0;
}

这道题有点意思，用了三次swap

月份天数

#include <iostream>
#include <cstdio>
#include <iomanip>
using namespace std;
int main()
{
	int y, m;
	cin >> y >> m;

	//判断闰年
	int temp;
	if (y % 4 == 0 && y % 100 != 0)temp = 1;
	else if (y % 100 == 0 && y % 400 != 0)temp = 0;
	else if (y % 400 == 0)temp = 1;
	else temp = 0;

	if (m == 2) {
		if (temp == 1)cout << "29" << endl;
		else cout << "28" <<endl;
	}
	else if (m == 1 || m == 3 || m == 5 || m == 7 || m == 8 || m == 10 || m == 12) {
		cout << "31" << endl;
	}
	else {
		cout << "30" << endl;
	}


	return 0;
}

不高兴的津津

#include <iostream>
#include <cstdio>
#include <iomanip>
using namespace std;
int main()
{
	int week[8];
	for (int i = 1; i < 8; i++) {
		int s, e;
		cin >> s >> e;
		if (s + e > 8)week[i] = s + e;
		else week[i] = 0;
	}
	int m = 0;
	int n;
	for (int i = 1; i < 8; i++) {
		if (week[i] > m) {
			m = week[i];
			n = i;
		}
	}
	cout << n << endl;

	return 0;
}

买铅笔

#include <iostream>
#include <cstdio>
#include <iomanip>
#include <climits>
using namespace std;
int main()
{
	int n;
	cin >> n;
	int money = INT_MAX;
	for (int i = 0; i < 3; i++) {
		int num,s;
		cin >> num >> s;
		if (n % num == 0) {
			money = min(money, n / num * s);
		}
		else {
			money = min(money,(n / num + 1) * s);
		}
	}
	cout << money << endl;

	return 0;
}

注意头文件

三角形分类

#include <iostream>
#include <cstdio>
#include <iomanip>
#include <climits>
using namespace std;
int main()
{
	int a, b, c;
	cin >> a >> b >> c;
	//保证a,b,c的大小按从小到大排序
	if (a > b)swap(a, b);
	if (b > c)swap(b, c);
	if (a > b)swap(a, b);

	if (a + b <= c || c - a >= b) {
		cout << "Not triangle" << endl;
		return 0;
	}
	else {
		if (a * a + b * b == c * c)cout << "Right triangle" << endl;
		if (a * a + b * b > c * c)cout << "Acute triangle" << endl;
		if (a * a + b * b < c * c)cout << "Obtuse triangle" << endl;
		if (a == b || b == c) {
			cout << "Isosceles triangle" << endl;
			if (a == b && b == c) {
				cout << "Equilateral triangle" << endl;
			}
		}
	}

	return 0;
}

小玉家的电费

#include <iostream>
#include <iomanip> 
using namespace std;
int main()
{
	double n;
	cin>>n;
	cout<<fixed<<setprecision(1);
	if(n<=150)cout<<0.4463*n<<endl;
	else{
		if(n>=151 && n<=400){
			int z=n-150;
			cout<<150*0.4463+z*0.4663<<endl;
		}else if(n>400){
			cout<<(n-400)*0.5663+250*0.4663+150*0.4463<<endl;
		}
	}
	
	
	return 0;
}

小鱼的航程（改进版）

#include <iostream>
#include <cstdio>
#include <iomanip>
#include <climits>
using namespace std;
int main()
{
	int weekday, n;
	cin >> weekday >> n;
	int sum = 0;
	for (int i = 0; i < n; i++) {
		if (weekday != 6 && weekday != 7)sum += 250;
		if (weekday == 7)weekday = 1;
		else weekday++;
	}
	cout << sum << endl;

	return 0;
}

三角函数

#include <iostream>
#include <cstdio>
#include <iomanip>
#include <climits>
using namespace std;
int main()
{
	int a, b, c;
	cin >> a >> b >> c;
	//a,b,c按照从小到大的顺序排序
	if (a > b)swap(a, b);
	if (b > c)swap(b, c);
	if (a > b)swap(a, b);

	//约分，找最大公因子
	int max = 1;
	for (int i = 2; i <=a; i++) {
		if (a % i == 0 && c % i == 0)max = i;
	}


	cout << a/max << "/" << c/max << endl;

	return 0;
}

注意需要约分（最大公因子）

#include <iostream>
#include <cstdio>
#include <iomanip>
#include <climits>
using namespace std;
int main()
{
	int num = 0;
	int arr[10];
	for (int i = 0; i < 10; i++) {
		cin >> arr[i];
	}
	int height;
	cin >> height;
	height += 30;
	for (int i = 0; i < 10; i++) {
		if (arr[i] <= height)num++;
	}
	cout << num << endl;

	return 0;
}

ABC

#include <iostream>
#include <cstdio>
#include <iomanip>
#include <climits>
using namespace std;
int main()
{
	int arr[3];
	cin >> arr[0] >> arr[1] >> arr[2];
	int x = arr[0];
	int y = arr[1];
	int z = arr[2];
	if (x > y)swap(x, y);
	if (y > z)swap(y, z);
	if (x > y)swap(x, y);
	arr[0] = x;
	arr[1] = y;
	arr[2] = z;

	char A, B, C;
	cin >> A >> B >> C;
	int a = A - 'A';
	int b = B - 'A';
	int c = C - 'A';
	cout << arr[a] << " " << arr[b] << " " << arr[c] << endl;



	return 0;
}

ISBN号码

#include <iostream>
#include <cstdio>
#include <iomanip>
#include <climits>
using namespace std;
int main()
{
	int sum = 0;
	string s;
	cin >> s;
	int j = 1;
	for (int i = 0; i < s.size()-1;i++) {
		if (s[i] == '-')continue;
		sum += (s[i] - '0') * j;
		j++;
	}

	//需要在输出之前就判断，因为有可能给出的最后一位就是X
	char check = (sum % 11 == 10) ? 'X' : '0' + sum % 11;
	if (check == (s[s.size() - 1]))cout << "Right" << endl;
	else {
		for (int i = 0; i < s.size() - 1; i++) {
			cout << s[i];
		}
		if (sum % 11 != 10)cout << sum % 11 << endl;
		else cout << "X" << endl;
	}


	return 0;
}

特别需要注意一点

        题目给出的识别码可能已经是X了，这时候直接比较s的最后一位是否和它相同就好，而不是只比较数字的时候