#include <cstdio>
#include <iostream>
using namespace std;
int main()
{
    double n1,n2,n3,n4;
    cin >> n1 >> n2 >> n3 >> n4;
    double X = (n1 *2 + n2 * 3 + n3 * 4 + n4 * 1) / 10;
    printf("Media: %.1f\n", X);
    if(X >= 7.0)
    printf("Aluno aprovado.\n");
    else if(X < 5.0)
    printf("Aluno reprovado.\n");
    else if(X >= 5.0 && X < 7.0)
    {
        printf("Aluno em exame.\n");
        double Y;
        cin >> Y;
        printf("Nota do exame: %.1lf\n", Y); //若数字没读出来，可以检查下是不是输入格式有问题
        double Z = (X + Y) / 2;
        if(Z >= 5.0)
        printf("Aluno aprovado.\n");
        else
        printf("Aluno reprovado.\n");
        printf("Media final: %.1lf\n", Z);  //若数字没读出来，可以检查下是不是输入格式有问题
    }

    return 0;
}

#include <iostream>
#include <cstdio>
#include <cmath>
using namespace std;
int main()
{
    double a,b,c;
    cin >> a >> b >> c;
    double delta = b * b - 4 * a * c;
    if (delta < 0 || a == 0)
    cout << "Impossivel calcular" << endl;
    else
    {
        double r1 = (-b + sqrt(delta)) / (2 * a); //注意运算优先级
        double r2 = (-b - sqrt(delta)) / (2 * a);
        printf("R1 = %.5lf\n",r1);
        printf("R2 = %.5lf\n",r2);
    }
        return 0;
}

#include <iostream>
using namespace std;
int main()
{
    int a,b,c;
    cin >> a >> b >> c;
    int x = a, y = b, z = c;   //由于还要输出原来的顺序，所以可以再给些新的变量来储存
    if(a > b)   //交换位置
    {
        int t = a;
        a = b;
        b = t;
    }
    if(a > c)
    {
        int t = a;
        a = c;
        c = t;
    }
    if(b > c)
    {
        int t = b;
        b = c;
        c = t;
    }
    cout << a << endl << b << endl << c << endl << endl;
    cout << x << endl << y << endl << z << endl;

    return 0;
}

注意这里的交的个人所得税，包括每个部分交税的

#include <iostream>
#include <cstdio>
using namespace std;
int main()
{
    double x, sum = 0; //代表公民的工资 和 工资各部分交税的总和
    cin >> x;
    if (x > 2000)
    {
        double y = 3000;
        if (x < 3000) y = x;
        sum += (y - 2000) * 0.08;
    }
    if (x > 3000)
    {
        double y = 4500;
        if (x < 4500) y = x;
        sum += (y - 3000) * 0.18;
    }
    if (x > 4500)
    sum += (x - 4500) * 0.28;
    if (sum == 0)
    printf("Isento");
    else
    printf("R$ %.2lf\n",sum);

    return 0;
}

#include <iostream>
using namespace std;
int main()
{ 
    int a,b,c,d;
    cin >> a >> b >> c >> d;
    int start = a * 60 + b;  //把小时化为分钟更好做
    int end = c * 60 + d;
    int st = end - start;
    if(st < 0 )
    st = 1440 - start + end;
    if(start < end)
    printf("O JOGO DUROU %d HORA(S) E %d MINUTO(S)", st / 60, st % 60);
    else if(start == end)
    printf("O JOGO DUROU 24 HORA(S) E 0 MINUTO(S)");
    else
    printf("O JOGO DUROU %d HORA(S) E %d MINUTO(S)",st / 60, st % 60);

    return 0;
}

#include <iostream>
using namespace std;
int main()
{
    double a,b,c;
    cin >> a >> b >> c;
    if(b > a)        //排序
    {
        double t = a;
        a = b;
        b = t;
    }
    if(c > a)
    {
        double t = a;
        a = c; 
        c = t;
    }
    if(b > c)
    {
        double t = b;
        b = c;
        c = t;
    }
    if(a >= b + c)
    cout << "NAO FORMA TRIANGULO" << endl;
    else
    {
        if(a*a == b*b + c*c)
        cout << "TRIANGULO RETANGULO" << endl;
        if(a*a > b*b + c*c)
        cout << "TRIANGULO OBTUSANGULO" << endl;
        if(a*a < b*b + c*c)
        cout << "TRIANGULO ACUTANGULO" << endl;
        if(a == b && a == c && b == c) //三边相等，要同时满足
        cout << "TRIANGULO EQUILATERO" << endl;
        else if(a == b || a == c || b == c)
        cout << "TRIANGULO ISOSCELES" << endl;
    }


    return 0;
}

本题的条件要一个一个罗列出来，不能分类包含在一类里面

#include <iostream>
#include <cstdio>
using namespace std;
int main()
{
    double x,y;
    cin >> x >> y;
    if(x > 0 && y > 0)
    cout << "Q1" << endl;
    else if(x > 0 && y < 0)
    cout << "Q4" << endl;
    else if(x < 0 && y > 0)
    cout << "Q2" << endl;
    else if(x < 0 && y < 0) 
    cout << "Q3" << endl;
    else if(x == 0 && y == 0)
    cout << "Origem" << endl;
    else if(x > 0 || x < 0 && y == 0)
    cout << "Eixo X" << endl;
    else
    cout << "Eixo Y" << endl;
    return 0;
}

#include <iostream>
using namespace std;
int main()
{
    int ddd;
    cin >> ddd;
    if(ddd == 61)
    cout << "Brasilia" << endl;
    else if(ddd == 71)
    cout << "Salvador" << endl;
    else if(ddd == 11)
    cout << "Sao Paulo" << endl;
    else if(ddd == 21)
    cout << "Rio de Janeiro" << endl;
    else if(ddd == 32)
    cout << "Juiz de Fora" << endl;
    else if(ddd == 19)
    cout << "Campinas" << endl;
    else if(ddd == 27)
    cout << "Vitoria" << endl;
    else if(ddd == 31)
    cout << "Belo Horizonte" << endl;
    else
    cout << "DDD nao cadastrado" << endl;

    return 0;
}

#include <iostream>
using namespace std;
int main()
{
    int a,b,c,d;
    cin >> a >> b >> c >> d;
    if(b > c && d > a && c + d > a + b && c > 0 and d > 0 && a % 2 == 0)
    cout << "Valores aceitos" << endl;
    else
    cout << "Valores nao aceitos" << endl;

    return 0;
}

#include <iostream>
using namespace std;
int main()
{
    string n1,n2,n3;
    cin >> n1 >> n2 >> n3;
    if(n1 == "vertebrado")
    {
        if(n2 == "ave")
        {
            if(n3 == "carnivoro")
            cout << "aguia" << endl;
            else
            cout << "pomba" << endl;
        }
        else
        {
            if(n3 == "onivoro")
            cout << "homem" << endl;
            else
            cout << "vaca" << endl;
        }

    }
    else if(n1 == "invertebrado")
    {
        if(n2 == "inseto")
        {
            if(n3 == "hematofago")
            cout << "pulga" << endl;
            else
            cout << "lagarta" << endl;
        }
        else
        {
            if(n3 == "hematofago")
            cout << "sanguessuga" << endl;
            else
            cout << "minhoca" << endl;
        }
    }
    else
    cout << "erro" << endl;

    return 0;
}