Array traversal in C - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of array traversal with pointer arithmetic

What is the output of this C program?

C

#include <stdio.h>

int main() {
    int arr[] = {10, 20, 30, 40, 50};
    int *p = arr;
    for (int i = 0; i < 5; i++) {
        printf("%d ", *(p + i));
    }
    return 0;
}

A 10 20 30 40 50

B 50 40 30 20 10

C 10 20 30 40 0

D Compilation error

💡 Hint

Remember that pointer arithmetic moves through the array elements in order.

The pointer p points to the first element of the array. Adding i moves it to the i-th element. So *(p + i) accesses each element in order, printing 10 20 30 40 50.

❓ Predict Output

intermediate

Output of array traversal with index and pointer

What will be printed by this C code?

C

#include <stdio.h>

int main() {
    int arr[3] = {1, 2, 3};
    int *p = arr;
    for (int i = 0; i < 3; i++) {
        printf("%d ", p[i]);
    }
    return 0;
}

A 1 2 3

B 3 2 1

C 0 0 0

D Runtime error

💡 Hint

Pointer p points to the first element, so p[i] accesses elements by index.

Using p[i] is equivalent to *(p + i), so it prints the array elements in order: 1 2 3.

❓ Predict Output

advanced

Output of nested array traversal

What is the output of this C program?

C

#include <stdio.h>

int main() {
    int matrix[2][3] = {{1, 2, 3}, {4, 5, 6}};
    for (int i = 0; i < 2; i++) {
        for (int j = 0; j < 3; j++) {
            printf("%d ", matrix[i][j]);
        }
    }
    return 0;
}

A 1 4 2 5 3 6

B 1 2 3 4 5 6

C 6 5 4 3 2 1

D Compilation error

💡 Hint

The outer loop goes through rows, inner loop through columns.

The code prints each element row by row: first row 1 2 3, then second row 4 5 6.

❓ Predict Output

advanced

Output of pointer traversal with increment

What does this C program print?

C

#include <stdio.h>

int main() {
    int arr[] = {7, 8, 9};
    int *p = arr;
    for (int i = 0; i < 3; i++) {
        printf("%d ", *p++);
    }
    return 0;
}

A 7 7 7

B 9 8 7

C 7 8 9

D Compilation error

💡 Hint

The *p++ means print value at p, then move p to next element.

The pointer p starts at arr[0]. Each loop prints *p then increments p, so prints 7 8 9.

❓ Predict Output

expert

Value of variable after complex array traversal

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

C

#include <stdio.h>

int main() {
    int arr[4] = {2, 4, 6, 8};
    int *p = arr + 1;
    int sum = 0;
    for (int i = 0; i < 3; i++) {
        sum += *(p++);
    }
    printf("%d", sum);
    return 0;
}

A 14

B Runtime error

C 20

D 18

💡 Hint

Pointer p starts at arr[1], sum adds three elements from there.

p points to arr[1] = 4, then 6, then 8. Sum = 4 + 6 + 8 = 18.

Practice

1. What does array traversal mean in C programming?

easy

A. Adding elements to the array

B. Deleting elements from the array

C. Visiting each element of the array one by one

D. Sorting the array elements

Solution

1. Step 1: Understand the term 'array traversal'

   Array traversal means going through each element in the array in order.

2. Step 2: Match the definition with options

   Only Visiting each element of the array one by one describes visiting each element one by one, which is the correct meaning.

3. Final Answer:

   Visiting each element of the array one by one -> Option C

4. Quick Check:

   Array traversal = visiting elements [OK]

Hint: Traversal means visiting all elements one by one [OK]

Common Mistakes:

• Confusing traversal with adding or deleting elements
• Thinking traversal means sorting
• Assuming traversal skips elements

2. Which of the following is the correct syntax to traverse an array arr of size n in C?

easy

A. for(int i = 0; i < n; i++)

B. for(int i = 1; i <= n; i++)

C. for(int i = 1; i < n; i++)

D. for(int i = 0; i <= n; i++)

Solution

1. Step 1: Understand array indexing in C

   Arrays start at index 0 and go up to n-1 for size n.

2. Step 2: Check loop conditions

   The loop must start at 0 and run while i is less than n (not equal), so for(int i = 0; i < n; i++) is correct.

3. Final Answer:

   for(int i = 0; i < n; i++) -> Option A

4. Quick Check:

   Loop from 0 to n-1 = correct traversal [OK]

Hint: Loop from 0 to less than n for array traversal [OK]

Common Mistakes:

• Using <= n causes out-of-bounds error
• Starting loop at 1 misses first element
• Using wrong loop condition

3. What will be the output of the following code?

int arr[] = {5, 10, 15};
for(int i = 0; i < 3; i++) {
    printf("%d ", arr[i]);
}

medium

A. 5 10 15 0

B. 15 10 5

C. 10 15 5

D. 5 10 15

Solution

1. Step 1: Understand the array elements

   The array contains 5, 10, and 15 in order at indices 0, 1, and 2.

2. Step 2: Trace the loop output

   The loop prints elements from index 0 to 2 in order, so output is "5 10 15 "

3. Final Answer:

   5 10 15 -> Option D

4. Quick Check:

   Print elements in order = 5 10 15 [OK]

Hint: Prints elements in order from index 0 to n-1 [OK]

Common Mistakes:

• Reversing order of output
• Printing extra zero
• Starting loop at wrong index

4. Identify the error in the following code snippet for traversing an array arr of size 5:

for(int i = 0; i <= 5; i++) {
    printf("%d ", arr[i]);
}

medium

A. Loop condition should be i < 5 to avoid out-of-bounds access

B. Loop variable should start from 1 instead of 0

C. Array size should be 6 instead of 5

D. No error, code is correct

Solution

1. Step 1: Check loop condition

   The loop runs while i <= 5, so i goes from 0 to 5 inclusive (6 iterations).

2. Step 2: Analyze array indexing

   Array indices go from 0 to 4 for size 5. Accessing arr[5] is out-of-bounds and causes error.

3. Final Answer:

   Loop condition should be i < 5 to avoid out-of-bounds access -> Option A

4. Quick Check:

   Use i < size to avoid errors [OK]

Hint: Use i < size, not i <= size, to avoid out-of-bounds [OK]

Common Mistakes:

• Using <= instead of <
• Starting loop at 1
• Ignoring array size limits

5. Given an integer array arr of size n, write a code snippet to find the sum of all elements using array traversal. Which of the following is correct?

hard

A. int sum = 0;
for(int i = 1; i < n; i++) {
sum += arr[i];
}

B. int sum = 0;
for(int i = 0; i < n; i++) {
sum += arr[i];
}

C. int sum = 0;
for(int i = 0; i <= n; i++) {
sum += arr[i];
}

D. int sum = 0;
for(int i = n - 1; i >= 0; i--) {
sum += arr[i];
}

Solution

1. Step 1: Understand array indexing and loop range

   Array indices go from 0 to n-1, so loop must run i from 0 to less than n.

2. Step 2: Check each option for correctness

   int sum = 0; for(int i = 0; i <= n; i++) { sum += arr[i]; } uses i <= n, which accesses arr[n] (out-of-bounds). int sum = 0; for(int i = 1; i < n; i++) { sum += arr[i]; } starts at 1, missing arr[0]. int sum = 0; for(int i = n - 1; i >= 0; i--) { sum += arr[i]; } correctly sums all elements in reverse order, but the question asks for traversal in forward order. int sum = 0; for(int i = 0; i < n; i++) { sum += arr[i]; } correctly sums all elements from 0 to n-1 in forward order.

3. Final Answer:

   int sum = 0; for(int i = 0; i < n; i++) { sum += arr[i]; } -> Option B

4. Quick Check:

   Loop from 0 to n-1 sums all elements [OK]

Hint: Sum elements by looping i from 0 to less than n [OK]

Common Mistakes:

• Using i <= n causing out-of-bounds
• Starting loop at 1 missing first element
• Looping backwards with wrong indices