Lære Nested Loops | Exploring Loop Variations

Introduction to Nested Loops

Nested loops are loops placed inside other loops. In Java, you use nested loops when you want to repeat a set of actions within another repeated action. This is especially useful for working with multi-dimensional data, such as tables or grids, where you need to access elements in a row-by-row or column-by-column manner.

Why use nested loops

Handle multi-dimensional arrays or lists;
Process data in tables, grids, or matrices;
Generate patterns or complex repetitive structures.

How do nested loops work

When you use a loop inside another loop, the inner loop completes all its iterations for each single iteration of the outer loop. This means the inner loop "restarts" every time the outer loop moves to the next step.

Pseudocode example:

for (row = 1; row <= 3; row++) {
    for (col = 1; col <= 4; col++) {
        print("Row: " + row + ", Column: " + col);
    }
}

This pseudocode will print every combination of rows and columns in a 3x4 grid. Nested loops help you perform actions on every pair, triplet, or more complex combinations of data.

Task

Imagine you want to create a multiplication table from 1 to 5. Instead of calculating each product manually, you can use nested loops to automate the process. The outer loop represents the rows (numbers 1 to 5), and the inner loop represents the columns (also numbers 1 to 5). At each step, the program calculates the product of the current row and column and prints it in a grid-like format.

Main.java


              1234567891011121314
            
package com.example;

public class Main {
    public static void main(String[] args) {
        // Print a multiplication table from 1 to 5 using nested loops
        System.out.println("Multiplication Table (1 to 5):");
        for (int i = 1; i <= 5; i++) {
            for (int j = 1; j <= 5; j++) {
                System.out.print(i * j + "\t");
            }
            System.out.println(); // Move to the next line after each row
        }
    }
}

Code Explanation

Outer Loop (for int i = 1; i <= 5; i++)
- Iterates through the numbers 1 to 5 for the rows of the table;
Inner Loop (for int j = 1; j <= 5; j++)
- Iterates through the numbers 1 to 5 for the columns of the table;
Printing the Product (System.out.print(i * j + "\t"))
- Calculates the product of the current row (i) and column (j)
- Prints it with a tab \t to align the numbers in a table format
Moving to the Next Line (System.out.println())
- After finishing one row, this statement moves the cursor to the next line so the next row of the table can be printed below.

A nested loop is a loop inside another loop, useful for tasks that involve multiple dimensions like tables or grids. Using nested loops avoids writing repetitive code for each row and column.

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