C-style for loop in Bash Scripting - Step-by-Step Execution

Concept Flow - C-style for loop

Initialize variable

↓

Check condition

↓

Execute body

↓

Update variable

↩Back to Check condition

The loop starts by setting a variable, then checks a condition. If true, it runs the loop body, updates the variable, and repeats. If false, it stops.

Execution Sample

Bash Scripting

for ((i=0; i<3; i++)); do
  echo $i
done

This loop prints numbers 0, 1, and 2 by increasing i from 0 to 2.

Execution Table

Iteration	i (before check)	Condition (i<3)	Body executed	Output	i (after update)
1	0	True	Yes	0	1
2	1	True	Yes	1	2
3	2	True	Yes	2	3
4	3	False	No

💡 i reaches 3, condition 3<3 is False, loop stops

Variable Tracker

Variable	Start	After 1	After 2	After 3	Final
i	0	1	2	3	3

Key Moments - 3 Insights

Why does the loop stop when i equals 3?

Because the condition i<3 becomes false at iteration 4 (see execution_table row 4), so the loop does not run the body again.

When is the variable i updated in the loop?

i is updated after the loop body executes in each iteration (see execution_table column 'i (after update)').

What happens if the initial value of i is already 3?

The condition i<3 is false immediately, so the loop body never runs (like iteration 4 in the table).

Visual Quiz - 3 Questions

Look at the execution table, what is the value of i before the condition check in iteration 3?

A 2

B 3

C 1

D 0

💡 Hint

Check the 'i (before check)' column in row 3 of the execution_table.

At which iteration does the loop condition become false?

A Iteration 2

B Iteration 3

C Iteration 4

D Iteration 1

💡 Hint

Look at the 'Condition (i<3)' column and find where it is False.

If we change the loop to for ((i=0; i<=3; i++)), how many times will the loop body execute?

A 3 times

B 4 times

C 5 times

D 2 times

💡 Hint

Think about the condition i<=3 and compare with the variable_tracker values.

Concept Snapshot

C-style for loop syntax in bash:
for (( init; condition; update )); do
  commands
 done

- init runs once at start
- condition checked before each iteration
- loop runs while condition is true
- update runs after each iteration
- useful for counting loops

Full Transcript

A C-style for loop in bash scripting starts by initializing a variable, then checks a condition before each loop run. If the condition is true, the loop body runs, then the variable updates. This repeats until the condition is false. For example, 'for ((i=0; i<3; i++))' prints 0, 1, and 2. The loop stops when i reaches 3 because the condition i<3 is no longer true. The variable i changes after each loop body execution. If i starts at 3, the loop never runs because the condition is false from the start.