Bài 1:
#include <iostream>
using namespace std;
int main()
{
    cout<<"Hello World";
    return 0;
}
Bài 2:
#include <iostream>
using namespace std;
int main()
{
    int a,b,tong,tich,hieu;
    float thuong;
    cout<<"nhap a:";
    cin>> a;
    cout<<"nhap b:";
    cin>> b;
    cout<<"\ntong="<<a+b;
    cout<<"\nhieu="<<a-b;
    cout<<"\ntich="<<a*b;
    cout<<"\nthuong="<<(float)a/b;
    return 0;
}
Bài 3
#include <iostream>
using namespace std;
int main()
{
    float a;
    cout<<"nhap so a:";
    cin>> a;
    cout<<"phan nguyen cua so a="<<int(a);
    return 0;
}
Bài 4:
#include <iostream>
using namespace std;
int main()
{
    char a;
    cout<<"Ki tu can chuyen qua ASCII la:";
    cin>> a;
    cout<<"Ma ASCII cua "<< a <<"  la:"<<(int)a;
    return 0;
}