Algorithms and Flowcharts

Objective

Write algorithms with decision-making (branching, looping).

What is an Algorithm?

An algorithm is a finite sequence of well-defined, computer-implementable instructions, typically used to solve a class of problems. It's a step-by-step procedure for achieving a desired outcome.

Key Algorithm Concepts

• Sequence: Instructions executed in a specific order.
• Selection (Branching): Choosing a different path based on a condition (e.g., using if, else if, else).
• Iteration (Looping): Repeating a block of instructions multiple times (e.g., using for, while, do-while).

Flowcharts

Flowcharts are diagrams that visually represent the steps of an algorithm. They use standard symbols to show the flow of control.

Common Flowchart Symbols

Symbol	Meaning
	Start/Begin
	Process/Operation
	Decision/Condition
	Input/Output
	Arrow/Flow Line
	End/Stop

Algorithm Examples

Example 1: Check if a number is positive

Algorithm:

1. Start
2. Input a number
3. If the number is greater than 0, then go to step 3.
4. Otherwise, go to step 4.
5. Display "The number is positive".
6. Go to step 5.
7. Display "The number is not positive".
8. End

Example 2: Calculate the area of a rectangle

Algorithm:

1. Start
2. Input the length of the rectangle
3. Input the width of the rectangle
4. Calculate the area: Area = length × width
5. Display the area
6. End

Example 3: Find the largest of three numbers

Algorithm:

1. Start
2. Input three numbers (a, b, c)
3. Assume a is the largest
4. If b is greater than a, then assume b is the largest
5. If c is greater than b, then assume c is the largest
6. Display the largest number
7. End

Decision-Making (Branching) in Algorithms

if statements allow algorithms to make choices. The general structure is:

if (condition) then
    // Instructions to execute if the condition is true
else
    // Instructions to execute if the condition is false

Looping in Algorithms

Loops allow algorithms to repeat a block of instructions. Common types of loops include:

• For loop: Repeats a block of instructions a specific number of times.
• While loop: Repeats a block of instructions as long as a condition is true.
• Do-While loop: Repeats a block of instructions as long as a condition is true, even if the condition is initially false.

Example: Using a For Loop

Algorithm: Print numbers from 1 to 5

1. Start
2. For i = 1 to 5 do:
3. Display the value of i
4. End for
5. End

Example: Using a While Loop

Algorithm: Repeatedly ask for input until a specific value is entered.

1. Start
2. Input a number
3. While the number is not equal to 10 do:
4. Display "Enter a number (not 10): "
5. Input a number
6. End while
7. Display "You entered 10"
8. End