Why loops are needed in C - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to print numbers from 1 to 5 using a loop.

C

#include <stdio.h>

int main() {
    int i = 1;
    while ([1] <= 5) {
        printf("%d\n", i);
        i++;
    }
    return 0;
}

Drag options to blanks, or click blank then click option'

Ai

B5

C0

D10

Attempts:

3 left

💡 Hint

Common Mistakes

Using a fixed number instead of the loop variable in the condition.

Not using the variable that changes inside the loop.

The variable i is used to control the loop and print numbers from 1 to 5.

2fill in blank

medium

Complete the code to sum numbers from 1 to 10 using a for loop.

C

#include <stdio.h>

int main() {
    int sum = 0;
    for (int i = 1; i [1] 10; i++) {
        sum += i;
    }
    printf("Sum is %d\n", sum);
    return 0;
}

Drag options to blanks, or click blank then click option'

A<=

B>

C<

D==

Attempts:

3 left

💡 Hint

Common Mistakes

Using < instead of <=, which stops at 9.

Using == which only runs once.

The loop should include 10, so the condition uses <= to go up to 10.

3fill in blank

hard

Fix the error in the loop condition to print numbers from 0 to 4.

C

#include <stdio.h>

int main() {
    int count = 0;
    while (count [1] 5) {
        printf("%d\n", count);
        count++;
    }
    return 0;
}

Drag options to blanks, or click blank then click option'

A==

B>=

C>

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using > or >= which causes the loop not to run.

Using == which runs only once.

The loop should run while count is less than 5 to print 0 to 4.

4fill in blank

hard

Fill both blanks to create a loop that prints even numbers from 2 to 10.

C

#include <stdio.h>

int main() {
    for (int num = [1]; num [2] 10; num += 2) {
        printf("%d\n", num);
    }
    return 0;
}

Drag options to blanks, or click blank then click option'

A2

B1

C<=

D>

Attempts:

3 left

💡 Hint

Common Mistakes

Starting from 1 instead of 2.

Using > instead of <= which skips printing 10.

The loop starts at 2 and runs while num is less than or equal to 10 to print even numbers.

5fill in blank

hard

Fill all three blanks to create a loop that prints numbers from 5 down to 1.

C

#include <stdio.h>

int main() {
    for (int i = [1]; i [2] 1; i[3]) {
        printf("%d\n", i);
    }
    return 0;
}

Drag options to blanks, or click blank then click option'

A5

B>=

C--

D++

Attempts:

3 left

💡 Hint

Common Mistakes

Using ++ instead of -- which counts up instead of down.

Using < instead of >= which causes the loop to not run.

The loop starts at 5, runs while i is greater than or equal to 1, and decreases i by 1 each time.

Practice

1. Why do we use loops in C programming?

easy

A. To repeat a block of code multiple times easily

B. To store multiple values in a variable

C. To create new data types

D. To stop the program immediately

Solution

1. Step 1: Understand the purpose of loops

   Loops allow repeating the same code without writing it again and again.

2. Step 2: Compare options with loop purpose

   Only To repeat a block of code multiple times easily describes repeating code multiple times easily, which is the main reason for loops.

3. Final Answer:

   To repeat a block of code multiple times easily -> Option A

4. Quick Check:

   Loops repeat code = To repeat a block of code multiple times easily [OK]

Hint: Loops repeat actions to avoid rewriting code [OK]

Common Mistakes:

• Confusing loops with variables
• Thinking loops create new data types
• Believing loops stop the program

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

easy

A. for (int i = 0; i < 5; i++) { }

B. loop (i = 0; i < 5; i++) { }

C. for i = 0 to 5 { }

D. for i in range(5): { }

Solution

1. Step 1: Recall C for loop syntax

   The correct for loop in C uses parentheses with initialization, condition, and increment separated by semicolons.

2. Step 2: Check each option

   for (int i = 0; i < 5; i++) { } matches the correct C syntax: for (int i = 0; i < 5; i++) { }.

3. Final Answer:

   for (int i = 0; i < 5; i++) { } -> Option A

4. Quick Check:

   C for loop syntax = for (init; condition; increment) [OK]

Hint: C for loops use semicolons inside parentheses [OK]

Common Mistakes:

• Using Python or other language syntax
• Missing semicolons in for loop
• Using wrong keywords like 'loop'

3. What will be the output of this C code?

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

medium

A. 0 1 2 3

B. 1 2 3 4

C. 1 2 3

D. 3 2 1

Solution

1. Step 1: Analyze loop range and iterations

   The loop starts at i=1 and runs while i is less than or equal to 3, so it runs for i=1, 2, 3.

2. Step 2: Determine printed output

   Each iteration prints the current i followed by a space, so output is "1 2 3 "

3. Final Answer:

   1 2 3 -> Option C

4. Quick Check:

   Loop prints 1 to 3 = 1 2 3 [OK]

Hint: Check loop start, end, and printed values carefully [OK]

Common Mistakes:

• Starting loop from 0 instead of 1
• Including extra numbers beyond 3
• Printing in reverse order

4. Identify the error in this C loop code:

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

medium

A. Incorrect loop condition

B. Missing semicolon after printf statement

C. Variable i is not declared

D. for loop syntax is wrong

Solution

1. Step 1: Check syntax inside the loop

   The printf statement is missing a semicolon at the end, which is required in C.

2. Step 2: Verify other parts

   The loop condition and variable declaration are correct, and the for loop syntax is valid.

3. Final Answer:

   Missing semicolon after printf statement -> Option B

4. Quick Check:

   Missing semicolon causes syntax error [OK]

Hint: Every statement in C ends with a semicolon [OK]

Common Mistakes:

• Ignoring missing semicolon errors
• Thinking loop condition is wrong
• Assuming variable is undeclared

5. You want to print all even numbers from 2 to 10 using a loop in C. Which loop is best and why?

hard

A. Use nested loops to check each number from 2 to 10

B. Use a while loop starting at 1, increment by 1 until 10 and print if even

C. Use a do-while loop starting at 10, decrement by 2 until 2

D. Use a for loop starting at 2, increment by 2 until 10

Solution

1. Step 1: Understand the task

   We need to print even numbers from 2 to 10, which are 2,4,6,8,10.

2. Step 2: Evaluate loop options

   Use a for loop starting at 2, increment by 2 until 10 uses a for loop starting at 2 and increments by 2, directly printing even numbers efficiently.

3. Final Answer:

   Use a for loop starting at 2, increment by 2 until 10 -> Option D

4. Quick Check:

   For loop with step 2 prints evens directly [OK]

Hint: Increment by 2 in for loop to print evens directly [OK]

Common Mistakes:

• Using nested loops unnecessarily
• Starting from 1 and checking each number
• Using do-while with wrong direction