3. Program structure and flow

It is possible to write a program as a single unbroken block of code. The program begins with the first instruction then the next instruction is run and so on until the program ends with the last instruction being carried out.

Start

Do this

Do this

Do this

Do this

End

But in reality any non-trivial program will be more complicated than this.

The diagram shows a program that has loops. It also makes calls to several subroutines or functions. It may be periodically interrupted by other programs and then continue where it left off.

This path that the program follows is called the 'program flow'. As you can see, program flow can be simple or very complicated, depending on what it is asked to do. You can map out the program flow using a flowchart.