For loop in C - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to print numbers from 0 to 4.

C

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

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

A<=

B>=

C>

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using >= or > will cause the loop to not run as expected.

Using <= will print an extra number.

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

2fill in blank

medium

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

C

int sum = 0;
for (int i = 1; i [1] 6; i++) {
    sum += i;
}
printf("%d\n", sum);

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

A>=

B<=

C<

D>

Attempts:

3 left

💡 Hint

Common Mistakes

Using <= 5 instead of < 6 is correct but not in the options.

Using > or >= will cause the loop to not run.

The loop should run while i is less than 6 to include numbers 1 to 5.

3fill in blank

hard

Fix the error in the for loop condition to print even numbers from 2 to 10.

C

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

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

A<=

B>=

C<

D>

Attempts:

3 left

💡 Hint

Common Mistakes

Using < 10 will exclude 10 from the output.

Using > or >= will cause the loop to not run.

The loop should run while i is less than or equal to 10 to include 10.

4fill in blank

hard

Fill both blanks to create a for loop that prints numbers from 10 down to 1.

C

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

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

A10

B>

C>=

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Starting at 1 will not print numbers down from 10.

Using > excludes 1 from the output.

The loop starts at 10 and runs while i is greater than or equal to 1.

5fill in blank

hard

Fill all three blanks to create a for loop that prints squares of numbers from 1 to 5.

C

for (int [1] = 1; [2] [3] 5; [1]++) {
    printf("%d\n", [1] * [1]);
}

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

Ai

C<=

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using different variable names in the loop causes errors.

Using < instead of <= excludes 5.

The loop variable is i, and the loop runs while i is less than or equal to 5.

Practice

1. What does a for loop in C primarily do?

easy

A. Repeats a block of code a fixed number of times

B. Defines a new variable

C. Stops the program execution

D. Declares a function

Solution

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

   A for loop is designed to repeat a block of code multiple times based on a condition.

2. Step 2: Identify the correct description

   Among the options, only repeating code a fixed number of times matches the for loop's purpose.

3. Final Answer:

   Repeats a block of code a fixed number of times -> Option A

4. Quick Check:

   For loop = repeat code [OK]

Hint: For loops repeat code a set number of times [OK]

Common Mistakes:

• Confusing for loop with variable declaration
• Thinking for loop stops program
• Mixing for loop with function declaration

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

easy

A. for i = 0 to 5 { }

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

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

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

Solution

1. Step 1: Review standard for loop syntax in C

   The correct syntax is: for (initialization; condition; update) { body }

2. Step 2: Check each option

   for (int i = 0; i < 5; i++) { } matches the correct syntax with initialization, condition, and update in proper order.

3. Final Answer:

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

4. Quick Check:

   Syntax = for(init; cond; update) [OK]

Hint: For loop syntax: for(init; condition; update) [OK]

Common Mistakes:

• Using 'for i = 0 to 5' which is not C syntax
• Swapping condition and initialization
• Missing semicolons inside for parentheses

3. What is the output of this code?

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

medium

A. 3 2 1

B. 0 1 2 3

C. 1 2 3

D. 1 2 3 4

Solution

1. Step 1: Analyze the loop range

   The loop starts at i=1 and runs while i is less than or equal to 3, incrementing i by 1 each time.

2. Step 2: Determine printed values

   It prints i each time: 1, then 2, then 3, then stops.

3. Final Answer:

   1 2 3 -> Option C

4. Quick Check:

   Loop prints 1 to 3 [OK]

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

Common Mistakes:

• Starting loop at 0 instead of 1
• Including an extra number beyond 3
• Printing in reverse order

4. Identify the error in this for loop:

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

medium

A. Missing semicolon after printf statement

B. Missing increment operator in for loop update

C. Incorrect loop condition syntax

D. Variable i not declared

Solution

1. Step 1: Examine the for loop update part

   The update section is 'i' without increment operator, so i never changes.

2. Step 2: Understand the effect of missing increment

   Without 'i++' or similar, the loop runs infinitely or behaves incorrectly.

3. Final Answer:

   Missing increment operator in for loop update -> Option B

4. Quick Check:

   Update must change loop variable [OK]

Hint: For loop update must change variable (e.g., i++) [OK]

Common Mistakes:

• Forgetting to increment loop variable
• Confusing semicolon placement
• Assuming variable auto-increments

5. How can you use a for loop to print only even numbers from 2 to 10 inclusive in C?

hard

A. for(int i = 2; i <= 10; i += 2) { printf("%d ", i); }

B. for(int i = 0; i <= 10; i++) { if(i % 2 == 0) printf("%d ", i); }

C. for(int i = 2; i < 10; i++) { if(i % 2 == 0) printf("%d ", i); }

D. for(int i = 0; i <= 10; i += 3) { printf("%d ", i); }

Solution

1. Step 1: Understand the goal

   We want to print even numbers from 2 to 10 inclusive.

2. Step 2: Check each option

   for(int i = 2; i <= 10; i += 2) { printf("%d ", i); } starts at 2 and increments by 2, printing 2,4,6,8,10 exactly.

3. Final Answer:

   for(int i = 2; i <= 10; i += 2) { printf("%d ", i); } -> Option A

4. Quick Check:

   Increment by 2 prints evens directly [OK]

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

Common Mistakes:

• Using wrong increment step
• Off-by-one errors in loop condition
• Printing odd numbers by mistake