Programming in C++ is similar to programming in C#, however there are some differences as to how these programming languages expect you to write your source files.

Program 1 shows the ubiquitous Hello World! program in C++.

Program 1. Hello World!

#include <iostream>

using namespace std;

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

	return 0;
}

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The first two lines will be explained later, however, the first line does have two features of note:

• The term include suggests that something is being included in this program, and
• The io suggests input-output, that is, we are dealing with something which allows input (streaming from the keyboard or elsewhere) and output (streaming to the screen or to a file).

Next, we see what is termed a function in C++. A function in C++ allows the programmer to define a sequence of statements which define what a processor should do.

The properties of a function are defined by:

1. A name (in this case, main),
2. Arguments (input) required for the function to run is specified in parentheses after the function name. In this case, () indicates that this function requires no arguments,
3. Each function can return one value. The type of this value is specified before the function name, in this case, an int (or integer), and
4. A sequence of statements. These are specified between two braces { ... }.

This function has exactly two statements. These are described in the following two sections.

Statement 1

The cout stands for console output, or something which is to be printed to the screen. Whenever you see cout followed by any number of:

this indicates that A should be printed to the screen, followed by B, followed by C and finally, followed by D. In this case, two things are printed:

• A string of characters, that is, a sequence of keys to be printed verbatim on the screen. These are surrounded by a pair of double quotes "...", and
• The object endl which defines and end-of-line character, that is, an indicator that output should continue on a new line on the screen.

Program 2. Hello World returns...

#include <iostream>

using namespace std;

int main() {
	cout << "Hello World!" << endl << endl << "This is..."
	     << "my second..." << endl << "...program."
             << endl;

	return 0;
}

The output for this program, when run, is:

Hello World!

This is...mysecond...
...program.

One of the strings are highlighted to ensure it stands out. Of course, in reality, everything would be the same.

A few things to note in this code:

• We can string together as many objects we want to print to the screen as we want,
• The << does not place any spaces. If we wanted a space we have to explicitly add it.

Statement 2

The statement

indicates that this function exits (returns) at this point and the value of the function is the integer 0.

The main Function

As mentioned before, all¹ statements which are to be interpreted as instructions to the CPU must appear inside functions. The main function is used to indicate those statements which the CPU is meant to begin executing when the executable program is run.

In Programs 1 and 2, the main function tells the CPU to print some text to the screen and then the main function ends by returning 0. When the main function returns, the executable program exits. Thus, both Programs 1 and 2 would stop executing once they've printed the text to the screen.

¹ This should read almost all, however you will not be directly exposed to the special cases in this course.

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