Flowcharts are drawn to illustrate graphically how an algorithm works. This basic introduction to flowcharting deals with only six of the numerous symbols that are used by programmers. Arrows are used to show the direction of the flow from one element (or box) to the next.
There are two boxes which are called terminal points. These are the Start and Stop boxes.The Start box has no entry points, just an exit. To use a flowchart, always find the Start box and begin there. You then simply follow the paths indicated by the arrows, doing whatever is indicated in the boxes encountered along the way. When a Stop box is entered, the algorithm is ended. The Stop box has a single entrance and no exits.
A Process box is used to indicate where an action of some sort takes place. This usually involves changes in value, form or location of information. A Process box has a single entrance and a single exit. No change in the direction of the flow of the algorithm can happen inside a Process box.
In order to make an algorithm generally useful, there needs to be a way of providing data for the algorithm to work on. In computer programs, the information being provided is called the input. The Input box is drawn as an abstract picture of a keyboard. For the user of an algorithm to find out what has happened, some information needs to be given back to him/her. This is the job of the Output box. It was originally designed to look like a stylized cathode ray tube (CRT). Both of these boxes have a single entrance and a single exit, just like a Process box. In fact, the Input and Output boxes can be considered to be special instances of the Process box, because information is being transferred from one place to another.
An algorithm would be very boring if it consisted of just a sequence of steps. To allow for branching in algorithms, the Decision box is used. Information (either the result of input or calculation) is checked and a decision is made as to how the flow of the program is to continue. For this reason, a Decision box (and only a Decision box) can have more than one exit.