C Programming — while, do-while, break & continue

1

while Loop — Condition Checked First

0 – 15 min

A while loop repeats a block of code as long as a condition is true. Before every iteration, the condition is checked. If it is false from the very start, the body never runs at all.

Best for: when you do not know exactly how many times to repeat — only when to stop
Condition checked: BEFORE the body runs each time
Minimum runs: 0 — if condition starts false, body never executes

while loop — flowchart

while loop — basic example

while_basic.c

C

#include <stdio.h>

int main() {
    int n = 0;

    // Runs exactly 10 times: n = 0,1,2,...,9
    while (n < 10) {
        printf("n = %d\n", n);
        n++;    // IMPORTANT: update n or loop runs forever!
    }

    printf("Loop ended. n = %d\n", n);
    return 0;
}

terminal

output

n = 0
n = 1
n = 2
...
n = 9
Loop ended. n = 10

How the while loop works — step by step:

Check: Is n < 10? If yes → run body. If no → exit loop.
Run body: print n, then n++ (n becomes 1)
Go back to check: Is 1 < 10? Yes → run body again
Repeat until n = 10: Is 10 < 10? No → exit loop

⚠️ Always update the variable inside the while loop!
If you forget n++, the condition stays true forever — infinite loop. The program freezes. Always make sure something inside the loop moves toward making the condition false.

2

Infinite while Loop — while(1)

15 – 22 min

A while(1) loop runs forever because the condition is always true (1). This is intentional in many real programs — servers, game loops, and menus use infinite loops on purpose, controlled by a break statement inside.

while(1) — 1 is always truthy → loops forever
while(0) — 0 is always false → body never runs
Any non-zero value in C is considered true

Infinite loop example

infinite_loop.c

C

#include <stdio.h>

int main() {
    // This loop NEVER stops on its own
    while (1) {
        printf("This loop will run forever.\n");
    }
    return 0;  // never reached!
}

Controlled infinite loop — with break

controlled_infinite.c

C

#include <stdio.h>

int main() {
    int count = 0;

    // Start with "loop forever"
    while (1) {
        count++;
        printf("Loop iteration: %d\n", count);

        // break exits when we decide to stop
        if (count == 5) {
            printf("Stopping at 5!\n");
            break;
        }
    }
    printf("After loop. count = %d\n", count);
    return 0;
}

terminal

output

Loop iteration: 1
Loop iteration: 2
Loop iteration: 3
Loop iteration: 4
Loop iteration: 5
Stopping at 5!
After loop. count = 5

💡 while(1) is used in real-world programs for:
Server programs that keep listening for connections, game loops that keep running until the player quits, embedded systems (microcontrollers) that must run forever. The break statement is how you exit them.

3

do-while Loop — Body Runs First

22 – 38 min

The do-while loop is the opposite of while — it runs the body first, then checks the condition. This means the body always executes at least once, even if the condition is false from the start.

Syntax: do { body; } while (condition); — note the semicolon at the end!
Condition checked: AFTER the body runs
Minimum runs: 1 — always runs the body once
Best for: menus, input validation — things that must show at least once

do-while loop — flowchart (body runs BEFORE check)

do-while — count 0 to 10

do_while.c

C

#include <stdio.h>

int main() {

    // Initialization
    int i = 0;

    do {
        // Loop body executes FIRST
        printf("%d ", i);

        // Update expression
        i++;

    } while (i <= 10);   // condition checked AFTER body ← semicolon!

    printf("\nDone!\n");
    return 0;
}

terminal

output

0 1 2 3 4 5 6 7 8 9 10
Done!

while — may never run

int n = 10;

// condition false from start
while (n < 5) {
    printf("runs\n");
}
// prints NOTHING

do-while — always runs once

int n = 10;

// body runs BEFORE check
do {
    printf("runs\n");
} while (n < 5);
// prints "runs" ONCE

Infinite do-while

infinite_dowhile.c

C

#include <stdio.h>

int main() {
    // do-while version of an infinite loop
    do {
        printf("This loop will run forever.\n");
    } while (1);   // condition 1 = always true

    return 0;
}

💡 When to use do-while vs while:
Use do-while when the action must happen at least once — menus, asking for user input, game rounds.
Use while when you want to skip entirely if the condition is already false — reading files, processing data.

⚠️ Don't forget the semicolon after while!
} while (condition); — the semicolon at the end is mandatory in do-while.
Without it you get a compiler error. This is different from a regular while loop which has no semicolon.

4

break — Exit the Loop Immediately

38 – 48 min

The break directive halts the loop immediately — no more iterations happen. Execution jumps to the first line after the closing } of the loop. It works inside all three loop types: for, while, and do-while.

Exits the innermost loop only — if nested, only the inner loop breaks
Also used in switch statements to prevent fall-through
The code after the loop continues normally

break — stops loop at iteration 5

1

→

2

→

3

→

4

→

5 BREAK

→

6,7,8,9,10 never run

break — halt a loop early

break_demo.c

C

#include <stdio.h>

int main() {
    int n = 0;

    while (1) {   // infinite loop — but break will stop it
        n++;

        if (n == 10) {
            printf("Reached 10 — breaking!\n");
            break;   // exit the while loop immediately
        }

        printf("n = %d\n", n);
    }

    printf("After loop. n = %d\n", n);
    return 0;
}

terminal

output

n = 1
n = 2
n = 3
n = 4
n = 5
n = 6
n = 7
n = 8
n = 9
Reached 10 — breaking!
After loop. n = 10

break in for loop — find first match

break_search.c

C

#include <stdio.h>

int main() {
    int arr[] = {3, 7, 15, 2, 9, 42, 6};
    int target = 9;

    for (int i = 0; i < 7; i++) {
        printf("Checking arr[%d] = %d\n", i, arr[i]);

        if (arr[i] == target) {
            printf("Found %d at index %d!\n", target, i);
            break;   // stop — no need to check the rest
        }
    }
    return 0;
}

terminal

output

Checking arr[0] = 3
Checking arr[1] = 7
Checking arr[2] = 15
Checking arr[3] = 2
Checking arr[4] = 9
Found 9 at index 4!
← arr[5]=42 and arr[6]=6 are never checked

5

continue — Skip This Iteration Only

48 – 58 min

The continue directive skips the rest of the current iteration and jumps immediately to the next one. The loop does NOT exit — it keeps going. Only the current pass is interrupted.

In a while loop — jumps back to the condition check
In a for loop — jumps to the update step (i++), then checks condition
Useful for skipping unwanted values while keeping the loop running

continue — skips odd numbers, prints only even

1SKIP

2 ✓

3SKIP

4 ✓

5SKIP

6 ✓

7SKIP

8 ✓

continue — print only even numbers

continue_even.c

C

#include <stdio.h>

int main() {
    int n = 0;

    while (n < 10) {
        n++;

        // If n is odd — skip the printf below
        if (n % 2 == 1) {
            continue;   // jump back to while(n < 10) check
        }

        // Only reaches here if n is even
        printf("The number %d is even.\n", n);
    }

    return 0;
}

terminal

output

The number 2 is even.
The number 4 is even.
The number 6 is even.
The number 8 is even.
The number 10 is even.

continue in for loop — skip multiples of 3

continue_skip3.c

C

#include <stdio.h>

int main() {
    printf("Numbers 1-15 (skipping multiples of 3):\n");

    for (int i = 1; i <= 15; i++) {

        if (i % 3 == 0) {
            continue;   // skip 3, 6, 9, 12, 15 — jump to i++
        }

        printf("%d ", i);
    }
    printf("\n");
    return 0;
}

terminal

output

Numbers 1-15 (skipping multiples of 3):
1 2 4 5 7 8 10 11 13 14

💡 break vs continue — key difference:
break → exits the loop completely. No more iterations.
continue → skips the current pass only. Loop continues with next iteration.
Think of it: break = quit the game. continue = skip this round, play next round.

6

Full Comparison — All Loop Types

58 – 60 min

Feature	for	while	do-while
Condition checked	Before each run	Before each run	After each run
Minimum executions	0	0	1 always
Best for	Known count (1 to 10)	Unknown count (read until 0)	Menus, must run once
Infinite version	`for(;;)`	`while(1)`	`do{} while(1);`
Semicolon after?	No	No	Yes — required!
break works?	Yes	Yes	Yes
continue works?	Yes (goes to i++)	Yes (goes to condition)	Yes (goes to condition)

Q

Quick Quiz

Question 1 of 5

What is the minimum number of times a while loop body can execute?

Question 2 of 5

What is the key difference between while and do-while?

Question 3 of 5

What does break do inside a while loop?

Question 4 of 5

In this code — what gets printed?
while(n < 10) { n++; if(n%2==1){ continue; } printf("%d ", n); }

Question 5 of 5

Which is required in do-while that regular while does NOT need?

✓

Lesson Checklist

I understand while checks condition BEFORE running body
I know while loop minimum runs = 0 (may never execute)
I understand while(1) is intentional infinite loop
I understand do-while checks condition AFTER running body
I know do-while always runs at least once
I remember the semicolon at end of do-while
I know break exits the loop completely immediately
I know continue skips current iteration only — loop continues
I can use break with while(1) to make a controlled infinite loop
I completed the quiz