While loop in C - Mini Project: Build & Apply

Using a While Loop in C

📖 Scenario: You are helping a cashier count the number of customers entering a store. The cashier wants to keep track until 5 customers have entered.

🎯 Goal: Build a C program that uses a while loop to count from 1 to 5 and print each number, simulating counting customers.

📋 What You'll Learn

Create an integer variable called count and set it to 1

Create an integer variable called max_customers and set it to 5

Use a while loop with the condition count <= max_customers

Inside the loop, print the current value of count

Inside the loop, increase count by 1

After the loop, print "Counting complete!"

💡 Why This Matters

🌍 Real World

Counting events or items repeatedly until a condition is met is common in many real-world tasks, like counting customers, steps, or inventory.

💼 Career

Understanding loops is essential for programming jobs, as loops help automate repetitive tasks efficiently.

1

Create the count variable

Create an integer variable called count and set it to 1.

C

int count = 1;  // Your code here

Hint

Use int count = 1; to create the variable.

2

Create the max_customers variable

Add an integer variable called max_customers and set it to 5 below the count variable.

C

#include 

int main() {
    int count = 1;
    int max_customers = 5;  // Your code here
    return 0;
}

Hint

Use int max_customers = 5; to create the variable.

3

Write the while loop

Write a while loop with the condition count <= max_customers. Inside the loop, print the value of count using printf, then increase count by 1.

C

#include 

int main() {
    int count = 1;
    int max_customers = 5;
    // Your code here
    return 0;
}

Hint

Use while (count <= max_customers) and inside the loop use printf("%d\n", count); and count++;.

4

Print completion message

After the while loop, add a printf statement to print "Counting complete!".

C

#include 

int main() {
    int count = 1;
    int max_customers = 5;
    while (count <= max_customers) {
        printf("%d\n", count);
        count++;
    }
    // Your code here
    return 0;
}

Hint

Use printf("Counting complete!\n"); after the loop.

Practice

1. What does a while loop do in C programming?

easy

A. Repeats a block of code while a condition is true

B. Executes code only once regardless of condition

C. Runs code a fixed number of times without checking condition

D. Stops the program immediately

Solution

1. Step 1: Understand the purpose of a while loop

   A while loop runs repeatedly as long as its condition remains true.

2. Step 2: Compare options with the definition

   Only Repeats a block of code while a condition is true correctly describes this behavior.

3. Final Answer:

   Repeats a block of code while a condition is true -> Option A

4. Quick Check:

   While loop = repeat while condition true [OK]

Hint: While loops run only if condition is true before each repeat [OK]

Common Mistakes:

• Thinking while loop runs at least once even if condition is false
• Confusing while loop with for loop fixed iterations
• Believing while loop stops program immediately

2. Which of the following is the correct syntax for a while loop in C?

easy

A. while (condition) { /* code */ }

B. while condition { /* code */ }

C. while [condition] { /* code */ }

D. while: (condition) { /* code */ }

Solution

1. Step 1: Recall C while loop syntax

   The condition must be inside parentheses and the code block inside braces.

2. Step 2: Check each option

   Only while (condition) { /* code */ } uses correct parentheses and braces syntax.

3. Final Answer:

   while (condition) { /* code */ } -> Option A

4. Quick Check:

   Correct syntax uses parentheses and braces [OK]

Hint: Remember: while(condition) with parentheses and braces [OK]

Common Mistakes:

• Omitting parentheses around condition
• Using square brackets instead of parentheses
• Adding colon after while keyword

3. What is the output of this C code?

int i = 1;
while (i <= 3) {
    printf("%d ", i);
    i++;
}

medium

A. 0 1 2 3

B. 1 2 3 4

C. 3 2 1

D. 1 2 3

Solution

1. Step 1: Trace the loop variable values

   i starts at 1, prints 1, then increments to 2, prints 2, then 3, and stops after printing 3 because i becomes 4 and condition fails.

2. Step 2: Confirm printed output

   The printed numbers are "1 2 3 " with spaces after each number.

3. Final Answer:

   1 2 3 -> Option D

4. Quick Check:

   Prints 1 to 3 with spaces [OK]

Hint: Check loop start, end condition, and increments carefully [OK]

Common Mistakes:

• Including 4 in output by mistake
• Starting from 0 instead of 1
• Printing numbers in reverse order

4. Identify the error in this code snippet:

int i = 0;
while (i < 5)
    printf("%d ", i);

medium

A. Syntax error due to missing braces

B. Missing semicolon after while condition

C. Infinite loop because i is never updated

D. Variable i is not declared

Solution

1. Step 1: Analyze loop behavior

   Variable i starts at 0 and condition is i < 5, but i is never incremented inside the loop.

2. Step 2: Understand consequence

   Since i never changes, the condition stays true forever, causing an infinite loop.

3. Final Answer:

   Infinite loop because i is never updated -> Option C

4. Quick Check:

   Loop variable must change to avoid infinite loop [OK]

Hint: Always update loop variable inside while loop [OK]

Common Mistakes:

• Assuming loop ends without variable update
• Thinking missing braces cause syntax error here
• Ignoring infinite loop possibility

5. How can you modify this code to print all even numbers from 2 to 10 using a while loop?

int num = 1;
while (num <= 10) {
    printf("%d ", num);
    num++;
}

hard

A. Use a for loop instead of while loop

B. Initialize num to 2 and increment by 2 inside the loop

C. Initialize num to 0 and increment by 1 inside the loop

D. Keep num at 1 and print only if num % 2 == 0 without incrementing

Solution

1. Step 1: Set starting point and increment for even numbers

   Start num at 2 (first even number) and increase by 2 each time to get only even numbers.

2. Step 2: Modify loop accordingly

   Change initialization to num = 2 and inside loop do num += 2 instead of num++.

3. Final Answer:

   Initialize num to 2 and increment by 2 inside the loop -> Option B

4. Quick Check:

   Start at 2, add 2 each time for evens [OK]

Hint: Start at first even, add 2 each loop to get evens [OK]

Common Mistakes:

• Not incrementing num causing infinite loop
• Printing odd numbers by starting at 1
• Using for loop when question asks for while loop