While loop in R Programming - Step-by-Step Execution

Concept Flow - While loop

Initialize variable

↓

Check condition

|Yes↓

Execute loop body

↓

Update variable

Back to Check condition↓

Exit loop

↩Back to Check condition

The while loop starts by checking a condition. If true, it runs the loop body and updates variables, then checks again. It stops when the condition is false.

Execution Sample

R Programming

x <- 1
while (x <= 3) {
  print(x)
  x <- x + 1
}

This code prints numbers 1 to 3 by increasing x until the condition x <= 3 is false.

Execution Table

Step	x value	Condition (x <= 3)	Action	Output
1	1	TRUE	Print 1, x <- 2	1
2	2	TRUE	Print 2, x <- 3	2
3	3	TRUE	Print 3, x <- 4	3
4	4	FALSE	Exit loop

💡 x reaches 4, condition 4 <= 3 is FALSE, loop stops

Variable Tracker

Variable	Start	After 1	After 2	After 3	Final
x	1	2	3	4	4

Key Moments - 2 Insights

Why does the loop stop when x is 4 even though the loop body updates x after printing?

The condition is checked before each loop iteration (see Step 4 in execution_table). When x becomes 4, the condition x <= 3 is FALSE, so the loop exits before printing or updating again.

What happens if the initial value of x is greater than 3?

The condition is FALSE at the start, so the loop body never runs (no output). This is shown by the condition check before the first iteration.

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of x at Step 3?

A 3

B 2

C 4

D 1

💡 Hint

Check the 'x value' column in row for Step 3 in execution_table.

At which step does the condition become FALSE and the loop stops?

A Step 2

B Step 4

C Step 3

D Step 1

💡 Hint

Look at the 'Condition' column in execution_table to find when it is FALSE.

If we start with x <- 5, what will happen to the loop execution?

A Loop runs once and prints 5

B Loop runs infinitely

C Loop does not run at all

D Loop runs twice

💡 Hint

Refer to key_moments about initial condition check before loop body execution.

Concept Snapshot

while (condition) {
  # code to repeat
}

- Checks condition before each loop
- Runs code block if TRUE
- Stops when condition is FALSE
- Useful for repeating until a condition changes

Full Transcript

This visual trace shows how a while loop works in R. We start with x = 1. The loop checks if x is less or equal to 3. If yes, it prints x and adds 1 to x. This repeats until x becomes 4, when the condition fails and the loop stops. The variable tracker shows x changing from 1 to 4 step by step. Key moments explain why the loop stops before printing 4 and what happens if x starts bigger than 3. The quiz tests understanding of variable values and loop stopping conditions.