Array traversal in C

Introduction

Array traversal means looking at each item in an array one by one. It helps us use or check every element in the list.

When you want to print all items in a list.

When you want to find a specific value inside an array.

When you want to change or update every element in a list.

When you want to calculate something using all elements, like sum or average.

Syntax

C

#include <stdio.h>

int main() {
    int array_name[array_size] = {elements};
    int index;

    for (index = 0; index < array_size; index++) {
        // Access array_name[index] here
    }

    return 0;
}

The loop starts at index 0 because arrays in C start counting from zero.

The loop runs until index is less than the size of the array to avoid going outside the array.

Examples

This example prints all elements of the array 'numbers'.

C

#include <stdio.h>

int main() {
    int numbers[5] = {10, 20, 30, 40, 50};
    int i;

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

    return 0;
}

This example shows what happens if the array is empty. The loop does not run.

C

#include <stdio.h>

int main() {
    int i;

    for (i = 0; i < 0; i++) {
        // This loop will not run because array size is zero
    }

    printf("No elements to traverse.\n");
    return 0;
}

This example shows traversal of an array with only one element.

C

#include <stdio.h>

int main() {
    int single_element[1] = {99};
    int i;

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

    return 0;
}

Sample Program

This program prints the temperature for each day of the week by looking at each element in the 'temperatures' array.

C

#include <stdio.h>

int main() {
    int temperatures[7] = {23, 25, 22, 20, 24, 26, 21};
    int day_index;

    printf("Temperatures for the week:\n");
    for (day_index = 0; day_index < 7; day_index++) {
        printf("Day %d: %d degrees\n", day_index + 1, temperatures[day_index]);
    }

    return 0;
}

Important Notes

Time complexity is O(n) because we look at each element once.

Space complexity is O(1) because we only use a few extra variables.

A common mistake is going past the last index, which causes errors or crashes.

Use array traversal when you need to process or check every item in the list.

Summary

Array traversal means visiting each element in the array one by one.

Use a for loop starting at 0 and ending before the array size.

Always be careful not to go outside the array limits.

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