Var for variables (mutable) in Swift - Step-by-Step Execution

Concept Flow - Var for variables (mutable)

Declare var x = 5

↓

Use x in code

↓

Change x = 10

↓

Use new x value

↓

End

This flow shows how a mutable variable is declared, used, changed, and used again with the new value.

Execution Sample

Swift

var x = 5
print(x)
x = 10
print(x)

Declare a mutable variable x, print it, change its value, then print the new value.

Execution Table

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

💡 Code ends after printing the 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 x can be reassigned new values as shown in steps 1 and 3 of the execution_table.

What happens if we try to use x before declaring it?

The code would give an error because x is undefined before step 1; variables must be declared before use.

Visual Quiz - 3 Questions

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

A 5

B 10

C undefined

D 0

💡 Hint

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

At which step does the output first show the value 5?

A Step 1

B Step 3

C Step 2

D Step 4

💡 Hint

Look at the 'Output' column in the execution_table to find when 5 is printed.

If we change 'var x = 5' to 'let x = 5', what would happen at step 3?

A Error because let variables cannot be changed

B x changes to 10 successfully

C x becomes 0

D No output is printed

💡 Hint

Recall that let declares constants which cannot be reassigned, unlike var.

Concept Snapshot

var declares a mutable variable in Swift.
You can assign a value and later change it.
Syntax: var variableName = value
Changing the value is allowed: variableName = newValue
Use var when you need to update the variable.

Full Transcript

This example shows how to use var in Swift to create a variable that can change. First, we declare x with var and assign 5. Then we print x, which outputs 5. Next, we change x to 10 and print again, outputting 10. The key point is var allows changing the variable's value after declaration. If we used let instead, changing x would cause an error. This helps understand mutable variables in Swift.