Explicit type annotation in Swift - Step-by-Step Execution

Concept Flow - Explicit type annotation

Declare variable

↓

Add explicit type annotation

↓

Assign value matching type

↓

Use variable in code

↓

Compile checks type correctness

↓

Run program with typed variable

This flow shows how you declare a variable with a specific type, assign a matching value, and then use it safely in your Swift code.

Execution Sample

Swift

var age: Int = 30
print(age)

Declare an integer variable 'age' with explicit type annotation and print its value.

Execution Table

Step	Action	Variable	Type Annotation	Value	Output
1	Declare variable with type	age	Int	uninitialized
2	Assign value 30	age	Int	30
3	Print variable	age	Int	30	30
4	End of program

💡 Program ends after printing the value of 'age'.

Variable Tracker

Variable	Start	After Assignment	Final
age	uninitialized	30	30

Key Moments - 2 Insights

Why do we write ': Int' after the variable name?

The ': Int' tells Swift that 'age' must always hold an integer. This is shown in the execution_table step 1 where the type is set explicitly.

What happens if we assign a value of a different type?

Swift will give a compile error because the value does not match the declared type. This is checked before step 3 in the execution flow.

Visual Quiz - 3 Questions

Look at the execution_table at step 2, what is the value of 'age'?

A uninitialized

B 30

C "30" as a string

D nil

💡 Hint

Check the 'Value' column at step 2 in the execution_table.

At which step is the variable 'age' first given a value?

A Step 2

B Step 1

C Step 3

D Step 4

💡 Hint

Look at the 'Action' column for when assignment happens in the execution_table.

If we remove ': Int' from the declaration, what changes in the execution?

A The program will not compile

B The variable becomes a string

C Swift infers the type automatically

D The variable cannot be used

💡 Hint

Swift can infer types if explicit annotation is missing, so check the concept_flow about type annotation necessity.

Concept Snapshot

Explicit type annotation in Swift:
var variableName: Type = value
- Declares variable with fixed type
- Helps catch type errors early
- Makes code clearer and safer
- Example: var age: Int = 30

Full Transcript

This visual execution shows how explicit type annotation works in Swift. First, a variable 'age' is declared with type Int. Then, the value 30 is assigned to it. The program prints the value 30. The type annotation ': Int' ensures the variable only holds integers, preventing errors. If a different type is assigned, Swift will stop compilation. This helps keep code safe and clear.