Algorithm

An algorithm is usually written as numbered steps. It states what input is needed, what actions must be performed and what result must be produced. It is useful for explaining a short solution in ordinary language.

Flowchart

A flowchart presents the steps as a diagram. Rectangles show processing, diamonds show decisions and arrows show the direction of execution. It is useful when we need to see different choices or repeated paths. Large charts can be difficult to draw and change.

Pseudocode

Pseudocode uses structured text such as READ, IF, WHILE and OUTPUT. It is useful for writing longer logic before choosing the exact C syntax. It is generally easier to edit than a large diagram.

Example: sum of two numbers

The algorithm says: read two numbers, add them and display the sum. Pseudocode writes the same actions using named variables. The flowchart uses Start, input, process, output and End symbols. All three must describe the same calculation.

READ a, b
sum ← a + b
OUTPUT sum

Important difference

The solution itself does not change when its presentation changes. For example, a condition must not become its opposite when it is copied from pseudocode to a flowchart. Check that the starting values, conditions and output agree in every version. None of these ordinary descriptions is automatically an executable C program.

Reference table

Key points

• The algorithm is the logic, rather than a particular drawing format.
• Different representations must agree on decisions and results.