Range operators (... and ..<) in Swift - Step-by-Step Execution

Concept Flow - Range operators (... and ..<)

Start

↓

Define range using ... or ..<

↓

Check range type

↓

... inclusive

↓

Generate numbers including end

↓

Use range in loop or array

↓

End

This flow shows how Swift uses ... for inclusive ranges and ..< for exclusive ranges to generate sequences of numbers.

Execution Sample

Swift

for i in 1...3 {
    print(i)
}

for j in 1..<3 {
    print(j)
}

This code prints numbers 1 to 3 inclusive with ... and 1 to 2 with ..<.

Execution Table

Step	Variable	Range Type	Value	Action	Output
1	i	1...3 (inclusive)	1	Print i	1
2	i	1...3 (inclusive)	2	Print i	2
3	i	1...3 (inclusive)	3	Print i	3
4	i	1...3 (inclusive)	4	Check condition fails
5	j	1..<3 (exclusive)	1	Print j	1
6	j	1..<3 (exclusive)	2	Print j	2
7	j	1..<3 (exclusive)	3	Check condition fails

💡 Loops stop when the variable reaches the end of the range (inclusive for ..., exclusive for ..<).

Variable Tracker

Variable	Start	After 1	After 2	After 3	Final
i	-	1	2	3	Loop ends after 3
j	-	1	2	-	Loop ends before 3

Key Moments - 2 Insights

Why does the loop with 1...3 include the number 3 but the loop with 1..<3 does not?

The execution_table shows that the ... operator includes the end value (3), so the loop prints 3. The ..< operator excludes the end value, so the loop stops before reaching 3.

What happens if we try to use ..< with the same start and end number, like 3..<3?

The loop will not run because the start is equal to the end and ..< excludes the end, so the condition is false immediately, as seen in the exit conditions in the execution_table.

Visual Quiz - 3 Questions

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

A 3

B 2

C 4

D 1

💡 Hint

Check the row where Step is 3 and Variable is i in the execution_table.

At which step does the loop with j in 1..<3 stop running?

A Step 6

B Step 5

C Step 7

D Step 4

💡 Hint

Look for the step where the condition fails for variable j in the execution_table.

If we change the range 1..<3 to 1...3 for variable j, how would the output change?

A It would exclude the number 2

B It would include the number 3 in the output

C It would print only number 1

D It would not print anything

💡 Hint

Compare the outputs for i and j in the execution_table to see the difference between ... and ..<.

Concept Snapshot

Swift range operators:
- ... is inclusive (includes end value)
- ..< is exclusive (excludes end value)
Use in loops to generate sequences
Example: for i in 1...3 prints 1,2,3
for j in 1..<3 prints 1,2

Full Transcript

This lesson shows how Swift uses two range operators: ... and ..<. The ... operator creates a range that includes the last number, so a loop using 1...3 will print 1, 2, and 3. The ..< operator creates a range that excludes the last number, so a loop using 1..<3 will print 1 and 2 only. The execution table traces each step of the loops, showing variable values and when loops stop. Key points include understanding why the inclusive range includes the end number and the exclusive range does not. The visual quiz tests understanding of these differences by asking about variable values at specific steps and the effect of changing range operators.