Nested Loop

Part of the Fundamentals section of Coddy's Swift journey — lesson 49 of 86.

A nested loop is simply a loop inside another loop. The inner loop completes all its iterations for each single iteration of the outer loop.

for row in 1...3 {
    for col in 1...2 {
        print("Row \(row), Col \(col)")
    }
}
// Output:
// Row 1, Col 1
// Row 1, Col 2
// Row 2, Col 1
// Row 2, Col 2
// Row 3, Col 1
// Row 3, Col 2

For each value of row, the inner loop runs completely through all values of col. So with 3 outer iterations and 2 inner iterations, the code inside runs 6 times total (3 × 2).

Nested loops are commonly used to work with grid-like structures or to generate patterns.

Here's an example that prints a simple rectangle of asterisks:

for row in 1...2 {
    for col in 1...4 {
        print("*", terminator: "")
    }
    print("")  // Move to next line
}
// Output:
// ****
// ****

The terminator: "" prevents print from adding a newline, so asterisks appear on the same row. After the inner loop finishes, print("") moves to the next line.

Challenge

Easy

Read two integers from input: rows and cols. Use nested loops to print a grid of numbers where each cell displays the product of its row number and column number.

You will receive the following inputs:

First line: number of rows (e.g., "3")
Second line: number of columns (e.g., "4")

Requirements:

Use an outer loop for rows (1 to rows)
Use an inner loop for columns (1 to cols)
Print the product of the current row and column numbers
Separate values on the same row with a space
Each row should be on its own line

Hint: Use terminator: " " to keep values on the same line, then use print("") after the inner loop to move to the next line.

For example, if rows is 3 and cols is 4, the output should be:

1 2 3 4 
2 4 6 8 
3 6 9 12

Cheat sheet

A nested loop is a loop inside another loop. The inner loop completes all its iterations for each single iteration of the outer loop.

for row in 1...3 {
    for col in 1...2 {
        print("Row \(row), Col \(col)")
    }
}
// Output:
// Row 1, Col 1
// Row 1, Col 2
// Row 2, Col 1
// Row 2, Col 2
// Row 3, Col 1
// Row 3, Col 2

With 3 outer iterations and 2 inner iterations, the code runs 6 times total (3 × 2).

Nested loops are useful for grid-like structures and patterns:

for row in 1...2 {
    for col in 1...4 {
        print("*", terminator: "")
    }
    print("")  // Move to next line
}
// Output:
// ****
// ****

Use terminator: "" to prevent print from adding a newline, keeping output on the same line. Use print("") after the inner loop to move to the next line.

Try it yourself

let rows = Int(readLine()!)!
let cols = Int(readLine()!)!

// TODO: Write your code below
// Use nested loops to print a multiplication grid
// Outer loop: iterate through rows (1 to rows)
// Inner loop: iterate through columns (1 to cols)
// Print the product of row * column
// Use print(..., terminator: " ") to keep values on the same line
// Use print("") after the inner loop to move to the next line