Array initialization in C - Step-by-Step Execution

Concept Flow - Array initialization

Declare array variable

↓

Specify size or initializer

↓

Assign values to elements

↓

Array ready to use

This flow shows how an array is declared, given a size or values, and then ready for use.

Execution Sample

C

int arr[3] = {10, 20, 30};
// Initialize array with 3 elements

int arr2[5] = {1, 2};
// Remaining elements set to 0

This code creates arrays with initial values; missing values default to zero.

Execution Table

Step	Action	Array State	Explanation
1	Declare int arr[3]	[?, ?, ?]	Array of size 3 created, values undefined
2	Initialize arr with {10, 20, 30}	[10, 20, 30]	All elements assigned explicitly
3	Declare int arr2[5]	[?, ?, ?, ?, ?]	Array of size 5 created, values undefined
4	Initialize arr2 with {1, 2}	[1, 2, 0, 0, 0]	First two elements assigned, rest zeroed
5	End	[10, 20, 30] and [1, 2, 0, 0, 0]	Arrays ready for use

💡 Initialization complete; arrays contain assigned or default values

Variable Tracker

Variable	Start	After Step 2	After Step 4	Final
arr	undefined	[10, 20, 30]	[10, 20, 30]	[10, 20, 30]
arr2	undefined	undefined	[1, 2, 0, 0, 0]	[1, 2, 0, 0, 0]

Key Moments - 3 Insights

Why do some elements become zero when not all are initialized?

In step 4, arr2 is initialized with fewer values than its size. The remaining elements are automatically set to zero by the compiler, as shown in the execution_table row 4.

What happens if I declare an array without initializing it?

In steps 1 and 3, arrays are declared but not initialized, so their elements contain garbage (undefined) values until assigned.

Can I initialize an array without specifying its size?

Yes, but not shown here. If you omit size and provide values, the compiler sets size to the number of values. This example uses explicit sizes.

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of arr[1] after step 2?

A 20

B 10

C 30

D undefined

💡 Hint

Check execution_table row 2 under Array State

At which step does arr2 get its remaining elements set to zero?

A Step 2

B Step 3

C Step 4

D Step 5

💡 Hint

Look at execution_table row 4 explanation

If arr2 was declared as int arr2[3] = {1, 2}; how would the final array look?

A [1, 2, 3]

B [1, 2, 0]

C [1, 2, undefined]

D [0, 0, 0]

💡 Hint

Refer to variable_tracker for arr2 initialization pattern

Concept Snapshot

Array initialization in C:
- Declare with type and size: int arr[3];
- Initialize with values: int arr[3] = {10, 20, 30};
- Missing values default to 0
- Uninitialized arrays contain garbage
- Arrays ready for use after initialization

Full Transcript

This lesson shows how arrays are created and initialized in C. First, an array is declared with a type and size. Then, values can be assigned using curly braces. If fewer values are given than the size, the rest become zero. If no values are given, the array contains undefined values. This is important to know so you don't use garbage data. The example shows two arrays: one fully initialized and one partially initialized with zeros filling the rest.