Hello world
A typical first program in many programming languages is called hello world and refers to a basic program that is only designed to display text to the screen. This program is meant to be used to illustrate some of the basic features of a programming language, such as syntax and style. The terms program, source code, and code can be used interchangeably.
For C++, the hello world program is as follows:
1 // This is a hello world program
2 #include <iostream>
3
4 using namespace std;
5
6 int main()
7 {
8 cout << "Hello world!" << endl;
9
10 return 0;
11 }
The following is a brief description of what each line is used for:
- Line 1: Lines that start with
//
are comments and are not technically part of the program but are often written to describe the code or insert other useful information such as the author. - Line 2: This is a preprocessor directive that includes the header file
iostream
which we need to usecout
andendl
on line 6. - Line 3: This is a blank line which is used to improve code readability.
- Line 4: This is a line that makes it easier to use commands in the standard
namespace
. This will be described in more detail later, but for now just know that it should be part of most programs that you write. - Line 5: Another blank line used to improve code readability.
- Line 6:
int main()
is the definition of the main body (or main function) that describes where the program actually starts. Every C++ program contains this function.int
refers to the fact that this function should return an integer to end it. - Line 7:
{
signifies the beginning of the main body block. - Line 8: This is a statement. Note that this code is indented. This is not technically required but improves code readability. Further details about this line are as follows:
-
cout
is used to display output to the terminal -
<<
is used to separate various things that will be displayed -
"Hello world!"
is astring
-
endl
is used to end the line on the output, going to the next line on the display -
;
is used to signify the end of the statement.
-
- Line 9: Another blank line used to improve code readability.
- Line 10:
return 0;
is the final line of the main body and returns an integer (in this case, 0) that matches line 6. - Line 11:
}
signifies the end of the main body. Note that this lines up in the same column as line 7. - Note that programs do not contain actual line numbers as shown above; the addition of line numbers is a function of the Wiki software and helps in referring to specific lines in our descriptions..