Calculating and Processing Devices – SS1 Further Mathematics Lesson Note (Second Term)

A flowchart is a diagram that shows the steps of a solution to a problem, in order, using standard symbols and arrows.

Behavioural objectives

By the end of the lesson, students should be able to:

1. Define a flowchart.
2. Name and state the use of the common flowchart symbols.
3. State the advantages of flowcharts.
4. Explain how a flowchart helps in planning algorithms and solving problems.
5. Draw a simple flowchart for a given problem.

What is a flowchart?

A flowchart is a diagrammatical representation of a solution to a problem.

• Steps: each step of the solution is placed in a symbol.
• Arrows: they join the symbols and show the order in which the steps are done.
• Use: it is drawn before a program is written, so the solution can be checked first.

What is an algorithm?

An algorithm is a finite list of clear steps for solving a problem.

• Algorithm: the steps written in words.
• Flowchart: the same steps drawn as a diagram.

What are the common flowchart symbols?

There are five common flowchart symbols: terminal, input/output, process, decision and flow line.

What are the advantages of flowcharts?

1. Programming: a flowchart plays an important role in computer programming.
2. Problem solving: it facilitates the interpretation and solution of problems.
3. Clarity: it can be easily understood.
4. Planning: it can help in the planning and development of algorithms for solving problems.

What are the limits of flowcharts?

• Size: a flowchart for a long, complex problem becomes large and hard to follow.
• Changes: if the solution changes, the diagram must be redrawn.

What are the rules for drawing a flowchart?

1. Begin with one Start symbol and end with one Stop symbol.
2. Use the standard symbols only.
3. Draw flow lines with arrowheads, usually top to bottom or left to right.
4. Write short, clear words inside each symbol.
5. Label the two exits of a decision symbol Yes and No.
6. Keep the lines from crossing one another.

How do we draw a flowchart? Worked examples

Example 1: Add two numbers

The problem is to find and display the sum of two numbers, A and B.

1. Start.
2. Input A and B.
3. Calculate Sum = A + B.
4. Output Sum.
5. Stop.

Example 2: Pass or fail

The problem is to decide whether a student passes, given a pass mark of 50.

1. Start.
2. Input the student’s score.
3. Decision: is the score 50 or more?
4. If Yes, output “Pass”.
5. If No, output “Fail”.
6. Stop.

Evaluation

1. What is a flowchart?
2. State four advantages of flowcharts.
3. How does a flowchart help in solving problems?
4. Name the flowchart symbol used for a decision and the symbol used for Start and Stop.
5. List the steps in a flowchart that adds two numbers and displays the answer.

Assignment

Draw a flowchart that inputs two numbers, finds their average, and displays the result.