Array initialization in C++ - Step-by-Step Execution

Concept Flow - Array initialization

Declare array variable

↓

Allocate memory for array

↓

Assign initial values

↓

Array ready to use

This flow shows how an array is declared, memory allocated, values assigned, and then ready for use.

Execution Sample

C++

#include <iostream>
using namespace std;

int main() {
  int arr[3] = {10, 20, 30};
  for(int i=0; i<3; i++) {
    cout << arr[i] << " ";
  }
  return 0;
}

This code creates an array of 3 integers, initializes it with values, and prints each value.

Execution Table

Step	Action	Array State	Index i	Output
1	Declare array arr[3]	[?, ?, ?]	-	-
2	Initialize arr[0] = 10	[10, ?, ?]	-	-
3	Initialize arr[1] = 20	[10, 20, ?]	-	-
4	Initialize arr[2] = 30	[10, 20, 30]	-	-
5	Start loop i=0	[10, 20, 30]	0	10
6	Loop i=1	[10, 20, 30]	1	20
7	Loop i=2	[10, 20, 30]	2	30
8	Loop i=3 condition false	[10, 20, 30]	3	-

💡 Loop ends when i reaches 3, condition i<3 is false

Variable Tracker

Variable	Start	After Step 5	After Step 6	After Step 7	Final
arr	[?, ?, ?]	[10, 20, 30]	[10, 20, 30]	[10, 20, 30]	[10, 20, 30]
i	-	0	1	2	3

Key Moments - 3 Insights

Why does the array show [?, ?, ?] before initialization?

Before assigning values, the array memory is allocated but contains garbage or unknown values, shown as '?'. Initialization fills these with known values (see steps 2-4).

Why does the loop stop when i equals 3?

The loop condition is i < 3. When i becomes 3, the condition is false, so the loop stops (see step 8). This prevents accessing outside the array bounds.

Why do we print arr[i] inside the loop?

Printing arr[i] inside the loop outputs each element one by one as i changes from 0 to 2 (steps 5-7). This shows the array contents in order.

Visual Quiz - 3 Questions

Look at the execution table, what is the value of arr after step 3?

A [10, ?, ?]

B [10, 20, ?]

C [?, ?, ?]

D [10, 20, 30]

💡 Hint

Check the 'Array State' column at step 3 in the execution table.

At which step does the loop condition become false?

A Step 8

B Step 7

C Step 5

D Step 4

💡 Hint

Look for the step where 'Loop i=3 condition false' appears in the execution table.

If we change the array size to 4 but keep the loop condition i<3, how many elements will be printed?

A 4 elements

B 0 elements

C 3 elements

D Depends on initialization

💡 Hint

The loop runs while i<3, so it prints 3 elements regardless of array size (see variable i in variable_tracker).

Concept Snapshot

Array initialization in C++:
int arr[size] = {val1, val2, ...};
- Declares array with fixed size
- Assigns initial values in order
- Uninitialized elements (if any) hold garbage
- Use loops to access elements safely
- Loop condition must prevent out-of-bounds access

Full Transcript

This visual trace shows how an array is declared and initialized in C++. First, memory is allocated for the array with unknown values. Then each element is assigned a value in order. A loop runs from 0 to size-1 to print each element. The loop stops when the index reaches the array size, preventing out-of-bounds access. Variables arr and i change as shown in the tables. Key moments clarify common confusions about initialization and loop stopping conditions.