Var for mutable references in Kotlin - Step-by-Step Execution

Concept Flow - Var for mutable references

Declare var x = 5

↓

x holds value 5

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Change x = 10

↓

x now holds value 10

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Use x in expressions

↓

Program continues

This flow shows how a variable declared with var can be changed to hold different values during program execution.

Execution Sample

Kotlin

var x = 5
println(x)
x = 10
println(x)

This code declares a mutable variable x, prints its initial value, changes it, then prints the new value.

Execution Table

Step	Action	Variable x	Output
1	Declare var x = 5	5
2	Print x	5	5
3	Assign x = 10	10
4	Print x	10	10
5	End of program	10

💡 Program ends after printing updated value of x

Variable Tracker

Variable	Start	After Step 1	After Step 3	Final
x	undefined	5	10	10

Key Moments - 2 Insights

Why can we change the value of x after declaring it with var?

Because var declares a mutable variable, so its value can be updated as shown in steps 1 and 3 of the execution_table.

What would happen if x was declared with val instead of var?

Declaring x with val makes it immutable, so trying to assign a new value like in step 3 would cause a compile error.

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of x after step 3?

A 5

B undefined

C 10

D Error

💡 Hint

Check the 'Variable x' column at step 3 in the execution_table.

At which step is the first output produced?

A Step 2

B Step 1

C Step 3

D Step 4

💡 Hint

Look at the 'Output' column in the execution_table to find when output first appears.

If we change var x = 5 to val x = 5, what happens at step 3?

A x changes to 10

B Compile error

C x remains 5 silently

D Runtime error

💡 Hint

Recall that val means immutable; reassigning causes a compile error.

Concept Snapshot

var declares a mutable variable in Kotlin
You can change its value anytime after declaration
Use var when you need to update the variable
val declares an immutable variable (cannot change)
Changing a var variable updates its stored value
Printing shows current value at that moment

Full Transcript

This example shows how to use var in Kotlin to create a mutable variable named x. Initially, x is set to 5. When we print x, it outputs 5. Then we change x to 10. Printing x again outputs 10. The key point is that var allows the variable to be changed after it is declared. If we used val instead, trying to change x would cause an error. The execution table tracks each step, showing the value of x and any output. The variable tracker shows how x changes from undefined to 5, then to 10. This helps beginners see how mutable variables work in Kotlin.