Lesson 05 of 20

6 mins read

Loops (For, While, Do-While) & Jump Statements

In Plain English

C provides 3 core iteration constructs: for loops for bounded iteration, while loops for precondition polling, and do-while loops for at-least-once execution. Use continue to skip cycles and break to terminate immediately.

The Mental Model

"A for loop is a fixed 100-meter sprint; a while loop is jogging until it starts raining; a do-while loop is taking at least one sip of soup before deciding if it is too hot."

Deep Dive: How It Works

for Loop: Composed of initialization, condition check, and increment expression.

while Loop: Evaluates condition before executing the loop body.

do-while Loop: Guarantees execution at least once before testing condition.

Syntax Blueprint

for (int i = 0; i < N; i++) {
    if (i == 2) continue;
    printf("%d\n", i);
}

Standard indexed iteration loop with continue to skip to the next iteration.

Core Rules to Remember

for Loop Mechanics: Ideal when step count and boundaries are known at compile or run time.

continue vs break: continue skips the rest of the current iteration; break exits the loop immediately.

Accumulation Patterns: Initialize accumulators to 0 before the loop to avoid reading uninitialized stack memory.

Common Beginner Traps & How to Fix Them

Mistake:Off-by-one errors with <= vs <.

Why it happens: Iterating for (int i = 0; i <= size; i++) over an array of length size accesses invalid memory.

How to fix: Use i < size for 0-indexed structures.

Pro Tip: Prefer for loops for indexed traversal so iteration variable scope is confined to the loop block.

Live Interactive Example

Hit Run Code to see it live

Filter Multiples with Continue

C11 / GCC 9.2

Output Console

Click "Run Code" to view the rendered output.

How it works: Numbers not divisible by 3 trigger continue, printing only 3, 6, 9, 12, and 15.

Your Turn: Micro Challenge

No pressure! Edit the starter code below and test your solution with instant feedback.

Micro Exercise

Calculate Range Sum with For Loop

Calculate the sum of integers from 1 to 5 inclusive using a second for loop.
Print "Sum: %d\n" with the calculated sum.

Sandbox Output

Click "Run & Check" to test your solution.

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