Array of structures - Step-by-Step Execution

Concept Flow - Array of structures

Define struct type

↓

Declare array of structs

↓

Initialize each struct element

↓

Access or modify elements

↓

Use elements in program

↓

End

This flow shows how you define a structure type, create an array of these structures, initialize each element, and then access or modify them.

Execution Sample

C

struct Point {
  int x;
  int y;
};

struct Point points[3];

points[0].x = 1;
points[0].y = 2;

This code defines a Point structure, creates an array of 3 Points, and sets the x and y values of the first element.

Execution Table

Step	Action	Variable/Element	Value/State	Explanation
1	Define struct Point	struct Point	Fields: x (int), y (int)	Structure type created with two int fields
2	Declare array	points[3]	Array of 3 Point structs (uninitialized)	Memory allocated for 3 Point elements
3	Assign points[0].x	points[0].x	1	Set x of first element to 1
4	Assign points[0].y	points[0].y	2	Set y of first element to 2
5	Examine points[1].x	points[1].x	uninitialized	No explicit assignment, remains uninitialized (garbage value)
6	Examine points[1].y	points[1].y	uninitialized	No explicit assignment, remains uninitialized (garbage value)
7	Examine points[2].x	points[2].x	uninitialized	No explicit assignment, remains uninitialized (garbage value)
8	Examine points[2].y	points[2].y	uninitialized	No explicit assignment, remains uninitialized (garbage value)
9	Access points[0]	points[0]	{x=1, y=2}	First element has assigned values
10	Access points[1]	points[1]	{x=uninitialized, y=uninitialized}	Second element remains uninitialized
11	Access points[2]	points[2]	{x=uninitialized, y=uninitialized}	Third element remains uninitialized
12	End	-	-	Program ends

💡 All array elements processed; program ends

Variable Tracker

Variable	Start	After Step 3	After Step 4	Final
points[0].x	uninitialized	1	1	1
points[0].y	uninitialized	uninitialized	2	2
points[1].x	uninitialized	uninitialized	uninitialized	uninitialized
points[1].y	uninitialized	uninitialized	uninitialized	uninitialized
points[2].x	uninitialized	uninitialized	uninitialized	uninitialized
points[2].y	uninitialized	uninitialized	uninitialized	uninitialized

Key Moments - 3 Insights

Why do points[1] and points[2] remain uninitialized?

Because we did not assign values to points[1] and points[2], their fields remain uninitialized and contain whatever was in memory (garbage values).

How do we access the fields of a struct inside an array?

Use the dot operator with the array index, like points[0].x, to access the x field of the first element.

Can we assign values to struct fields directly after declaring the array?

Yes, each element of the array is a struct, so you can assign to its fields individually using the dot operator.

Visual Quiz - 3 Questions

Look at the execution table, what is the value of points[0].y after step 4?

A 1

B 2

C 0

D uninitialized

💡 Hint

Check the 'Value/State' column for step 4 in the execution_table.

At which step do we assign a value to points[0].x?

A Step 3

B Step 4

C Step 2

D Step 5

💡 Hint

Look for the action 'Assign points[0].x' in the execution_table.

If we want to set points[2].y to 5, which step would that resemble?

A Step 6

B Step 7

C Step 8

D Step 9

💡 Hint

Step 8 is where points[2].y is examined in the execution_table.

Concept Snapshot

Array of structures in C:
- Define a struct type with fields.
- Declare an array of that struct type.
- Access elements with array[index].field.
- Assign or read fields individually.
- Uninitialized elements contain garbage values.

Full Transcript

This visual execution trace shows how to use an array of structures in C. First, we define a struct type named Point with two integer fields x and y. Then, we declare an array named points with 3 elements of type Point. We assign values to the fields of the first element points[0].x and points[0].y. The other elements remain uninitialized and may contain garbage values. We access each element's fields using the dot operator with the array index. This example helps beginners see how arrays of structs are created, initialized, and accessed step-by-step.