Hello World

//头文件 
#include<cstdio>//printf(),scanf()
#include<iostream>//cin<<,cout<<

using namespace std;

int main()
{
    cout << "Hello World!" << endl;
    
    return 0;
}

输入输出

scanf()，printf() 比 cin >>,cout << 效率高
endl：回车

a + b

#include<iostream>

using namespace std;

int main()
{
    int a,b;
    cin >> a >> b;
    cout << a + b << endl;
    
    return 0;
}

差

#include<cstdio>
#include<iostream>

 using namespace std;

 int main()
 {
     int a, b, c, d;
     cin >> a >> b >> c >> d ;
     cout << "DIFERENCA = " << a * b - c * d << endl;
     scanf("%d%d%d%d", &a,&b,&c,&d);
     printf("DIFERENCA = %d",a * b - c * d);

     return 0;
 }