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)

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.Arrays;

public class Main {
    public static void main(String[] args) {
        int[] int_list = {0, 4, 51, 83, 92, 10, 123, 145};
        int[] even = new int[4];
        int[] odd = new int[4];

        int evenIndex = 0;
        int oddIndex = 0;

        for (int item : int_list) {
            if (item % 2 == 0) {
                even[evenIndex] = item;
                evenIndex++;
            } else {
                odd[oddIndex] = item;
                oddIndex++;
            }
        }

        // Print the even and odd arrays
        System.out.println("Even numbers: " + Arrays.toString(even));
        System.out.println("Odd numbers: " + Arrays.toString(odd));
    }
}