For loop in C - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a nested for loop

What is the output of this C code snippet?

C

#include <stdio.h>

int main() {
    for (int i = 1; i <= 3; i++) {
        for (int j = 1; j <= 2; j++) {
            printf("%d%d ", i, j);
        }
    }
    return 0;
}

A Error: Syntax error

B 12 11 22 21 32 31

C 11 21 31 12 22 32

D 11 12 21 22 31 32

💡 Hint

Think about how the inner loop runs completely for each iteration of the outer loop.

The outer loop runs i from 1 to 3. For each i, the inner loop runs j from 1 to 2, printing i and j together. So the output is pairs: 11 12 21 22 31 32.

❓ Predict Output

intermediate

Value of variable after for loop

What is the value of variable sum after running this code?

C

#include <stdio.h>

int main() {
    int sum = 0;
    for (int i = 0; i < 5; i++) {
        sum += i;
    }
    printf("%d", sum);
    return 0;
}

A 10

B 15

C 5

D 0

💡 Hint

Add numbers from 0 to 4.

The loop adds 0+1+2+3+4 = 10 to sum.

🔧 Debug

advanced

Identify the error in the for loop

What error does this code produce when compiled or run?

C

#include <stdio.h>

int main() {
    int i;
    for (i = 0; i < 5; i++)
        printf("%d ", i);
    i = i + 1;
    return 0;
}

A No error, prints: 0 1 2 3 4

B Compilation error: missing braces

C Runtime error: segmentation fault

D No output

💡 Hint

Check if braces are required for single statement loops.

The for loop has one statement without braces, which is valid in C. The code prints numbers 0 to 4 with spaces.

❓ Predict Output

advanced

Output of a for loop with continue

What is the output of this code?

C

#include <stdio.h>

int main() {
    for (int i = 0; i < 5; i++) {
        if (i == 2) continue;
        printf("%d", i);
    }
    return 0;
}

A 01234

B 0134

C 024

D Error: continue outside loop

💡 Hint

The continue skips printing when i is 2.

When i is 2, continue skips the printf. So output is 0 1 3 4 without spaces.

🧠 Conceptual

expert

Number of iterations in a complex for loop

How many times will the loop body execute in this code?

C

#include <stdio.h>

int main() {
    int count = 0;
    for (int i = 1; i < 10; i *= 3) {
        count++;
    }
    printf("%d", count);
    return 0;
}

A 2

B 4

C 3

D 5

💡 Hint

Look at how i changes each time: 1, 3, 9, then stops.

i starts at 1, then 3, then 9. Next would be 27 which is not less than 10, so loop stops. So 3 iterations.