C++: The Basics

Here is a standard "Hello World" program, written in C++:

#include <iostream>
using std::cout;
using std::endl;

int main() {

  cout << "Hello world!" << endl;

  return 0;
}

When run, this program displays...you guessed it..."Hello World" to the standard output. (If you're running this program from the command line, standard output means the screen.)

Here's another little program that asks the user to enter two numbers and displays their sum:

#include <iostream>
using std::cout;
using std::cin;
using std::endl;

int main() {

  int number1 = 0;
  int number2 = 0;

  cout << "Enter a number: ";
  cin >> number1;

  cout << "Enter another number: ";
  cin >> number2;

  int result = number1 + number2;
  
  cout << number1 << " + " << number2 << " = " << result << endl;

  return 0;
}

This next bit of code displays information about two numbers if their sum is even:

#include <iostream>
using std::cout;
using std::endl;

int main() {

  for( int number1 = 0; number1 < 5; number1++ ) {
    for( int number2 = 0; number2 < 5; number2++ ) {

      // if the sum is even, print it out
      if( (number1+number2) % 2 == 0 ) {
	cout << number1 << " + " << number2 << " = " 
	     << (number1 + number2) << endl;
      }

    }
  }

  return 0;
}

Compiling using g++

To compile a program named myProg.cc with the GNU C++ compiler, type g++ -Wall -Werror -o myProg myProg.cc. This command takes your C++ file, named myProg.cc, compiles it, and creates an executable named myProg. You should be able to run your newly-created program by typing ./myProg on the command line.