Unit 4.2 - For Loops

4.2 For Loops

Similar to while loops, for loops run until a condition is false. Format of for loop below:

for (int i = 0; i < 5; i++) {
    System.out.println(i);
}

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Explanation

• in the above for loop:
  • int i = 0 defines the iterating variable
  • i < 5 is the condition (once i < 5 is false, this loop breaks)
  • i++ is the incrementation of the iterating variable
  • System.out.println(i); is the body code that runs every time the loop iterates

For Each Loops:

• Apart from iterating using an incrementing variable, you can also iterate through items in a list.

  Example of For Each loop below

int[] list = {1, 2, 3, 4, 5}; // any list
for (int item : list) { // for each item in the list, execute the body
    System.out.println(item); // body code
}

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#python version
array=[1, 2, 3, 4, 5]
for i in array:
    print(i)

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Explanation:

• in the above loop:
  • int item : list - this line is saying that for each item in the list, execute code below
  • System.out.println(num); - this line is the body code.

Fun For Loop Hack:

Create a program that iterates through a list of numbers (int_list = {0, 4, 51, 83, 92, 10, 123, 145}) using both a for loop and a for each loop, then split the numbers in the list into even/odd lists, and output them.

import java.util.ArrayList;

public class NumberSplitter {
    public static void main(String[] args) {
        int[] intList = {0, 4, 51, 83, 92, 10, 123, 145};

        ArrayList<Integer> evenNumbers = new ArrayList<>();
        ArrayList<Integer> oddNumbers = new ArrayList<>();

        System.out.println("Using traditional for loop:");
        for (int i = 0; i < intList.length; i++) {
            System.out.println(intList[i]);
            if (intList[i] % 2 == 0) {
                evenNumbers.add(intList[i]);
            } else {
                oddNumbers.add(intList[i]);
            }
        }

        evenNumbers.clear();
        oddNumbers.clear();

        System.out.println("\nUsing for-each loop:");
        for (int num : intList) {
            System.out.println(num);
            if (num % 2 == 0) {
                evenNumbers.add(num);
            } else {
                oddNumbers.add(num);
            }
        }

        System.out.println("\nEven numbers: " + evenNumbers);
        System.out.println("Odd numbers: " + oddNumbers);
    }
}
NumberSplitter.main(null);

Using traditional for loop:
0
4
51
83
92
10
123
145

Using for-each loop:
0
4
51
83
92
10
123
145

Even numbers: [0, 4, 92, 10]
Odd numbers: [51, 83, 123, 145]

Adjust Speed: 2
Adjust Size: 15

Iteration: 0

Current Velocity: 2, 2