Array traversal in C - Step-by-Step Execution

Concept Flow - Array traversal

Start: i = 0

↓

Check: i < array_length?

No→End traversal

Yes↓

Access array[i

↓

Process element

↓

Increment i

↩Back to Check

We start from the first element, check if the index is within bounds, access and process the element, then move to the next index until all elements are visited.

Execution Sample

C

#include <stdio.h>

int main() {
    int arr[] = {10, 20, 30};
    int n = 3;
    for (int i = 0; i < n; i++) {
        printf("%d\n", arr[i]);
    }
    return 0;
}

This code prints each element of the array one by one.

Execution Table

Iteration	i	Condition (i < n)	Action	Output
1	0	0 < 3 = True	Print arr[0] = 10	10
2	1	1 < 3 = True	Print arr[1] = 20	20
3	2	2 < 3 = True	Print arr[2] = 30	30
4	3	3 < 3 = False	Exit loop

💡 i reaches 3, condition 3 < 3 is False, loop ends

Variable Tracker

Variable	Start	After 1	After 2	After 3	Final
i	undefined	0	1	2	3
arr[i]	N/A	10	20	30	N/A

Key Moments - 3 Insights

Why does the loop stop when i equals the array length?

Because the condition i < n becomes false at i = 3 (see execution_table row 4), so the loop exits to avoid accessing outside the array.

What happens if we try to access arr[i] when i is equal to n?

Accessing arr[n] is out of bounds and causes undefined behavior. The loop condition prevents this by stopping before i reaches n (see execution_table).

Why do we start i from 0 instead of 1?

Array indexes in C start at 0, so the first element is arr[0]. Starting at 0 ensures we visit all elements correctly (see variable_tracker for i values).

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of i during the third iteration?

A 1

B 2

C 3

D 0

💡 Hint

Check the 'i' column in execution_table row 3.

At which iteration does the loop condition become false?

A Iteration 4

B Iteration 3

C Iteration 2

D Iteration 1

💡 Hint

Look at the 'Condition (i < n)' column in execution_table row 4.

If the array length n was 4 instead of 3, how many iterations would the loop run?

A 5

B 3

C 4

D 2

💡 Hint

The loop runs while i < n, so if n=4, i goes from 0 to 3 (4 iterations).

Concept Snapshot

Array traversal in C:
- Use a for loop: for(int i=0; i<n; i++)
- Start i at 0 (first index)
- Continue while i < n (array length)
- Access elements as arr[i]
- Stops before i reaches n to avoid out-of-bounds

Full Transcript

Array traversal means visiting each element of an array one by one. We start with an index i at 0, the first element. We check if i is less than the array length n. If yes, we access arr[i] and do something with it, like print it. Then we increase i by 1 and repeat. When i equals n, the condition fails and the loop stops. This prevents accessing outside the array, which is unsafe. The example code prints each element of the array. The execution table shows each step: the index i, the condition check, the action, and the output. The variable tracker shows how i and arr[i] change over time. Common confusions include why the loop stops at i = n, why we start at 0, and what happens if we access arr[n]. The quiz questions help check understanding of these steps.