Program:

    #include<iostream.h>
    #include<conio.h>

    void main()
    {
    int num,n,sum,r;
    clrscr();
    cout<<"\nEnter the number: \n";
    cin>>num;
    n=num;
    sum=0;
    while(n!=0)
    {
    r=n%10;
    sum+=(r*r*r);
    n/=10;
    }
    if(sum==num)
    cout<<num<<" is an Armstrong number";
    else
    cout<<num<<" is not an Armstrong number";
    getch();
    }