Getting Started with C++

Andrea Havron

About C++

• Created by Bjarne Stroustrup as an extension of the C language

• One of the world’s most popular programming language (lots of development resources online)

• Allows for object-oriented programming

• C++ is strongly typed, meaning the variable type must be defined before it is used

C++ Preliminaries

• Lines end in semi-colons

• Everything must be declared first, even functions

• Indexing starts at 0!!

• Basic math operators the same as R (=,+,-,/,*)

• Code must first be compiled before it is run

Basic Program

#include <iostream>
using namespace std;

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

• include <iostream>: allows the program to access the iostream library
• using namespace std: allows access to objects and variables from the standard library
  • if using namespace std not included, the user would need to specify std::cout
• int main:
  • int declares the type of the function named main
  • the type of the return (in this case, integer), must match the type of the function
• cout: prints a messages directly to the screen when the program is run

If a function is not expected to return a value, then void can be used. The above program can be re-written:

#include <iostream>
using namespace std;

void main() {
  cout << "Hello World!";
}

C++ Types

• bool: Boolean (lowercase: true or false)
• char: Character
• int: Integer
• float: Floating point
• double: Double floating point
• void: No return value

Simple Addition Program

The following program takes two integers as inputs and return an integer output:

int add(int x, int y) {
  x = 1;
  y = 2;
  return x + y;
}

The above program will fail if inputs are decimals. An additional program is needed to handle the different data type. The following will return a floating point output:

double add(double x, double y) {
  x = 1.2;
  y = 2.4;
  return x + y;
}

Vector Type

std::vector: vector from standard library

• The type is specified using the basic C++ types, i.e. std::vector is a vector of integers
• std::vector has a number of member functions that can be used to operate on the vector
  • begin: return iterator to beginning
  • end: return iterator to end
  • size: returns vector size
  • resize: changes the vector size
  • []: access element
  • front: access first element
  • back: access last element
  • push_back: append element to end
  • pop_back: delete last element
  • clear: clear content
  • for a more detailed list see here

The following program initializes a vector, resizes it, adds elements, and returns the vector:

#include <iostream>

std::vector<double> create_vector() {
  std::vector<double> x;
  x.resize(3);
  x[0] = 1.3;
  for(int i=1; i<3; i++){
    x[i] = x[i-1] + 1.3;
  }
  x.push_back(8.1);
  
  return x;
}

The above program returns the following vector of four: 1.3 2.6 3.9 8.1

Constants

If you don’t want a value to change throughout the program, you can assign constant

const int MinutesPerHour = 60;
const double pi = 3.14159;