Unit4.2

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.ArrayList;
import java.util.List;

        int[] intList = {0, 4, 51, 83, 92, 10, 123, 145};

        List<Integer> evenList = new ArrayList<>();
        List<Integer> oddList = new ArrayList<>();

        // this is the for loop part

        for (int i = 0; i < intList.length; i++) {
            if (intList[i] % 2 == 0) {
                evenList.add(intList[i]);
            } else {
                oddList.add(intList[i]);
            }
        }

        System.out.println("for loop:");
        System.out.println("even number list:" + evenList);
        System.out.println("odd number list:" + oddList);

        evenList.clear();
        oddList.clear();

        // below is the for each loop partt

        for (int num : intList) {
            if (num % 2 == 0) {
                evenList.add(num);
            } else {
                oddList.add(num);
            }
        }

        System.out.println("for each loop:");
        System.out.println("even number list: " + evenList);
        System.out.println("odd number list: " + oddList);

for loop:
even number list:[0, 4, 92, 10]
odd number list:[51, 83, 123, 145]
for each loop:
even number list: [0, 4, 92, 10]
odd number list: [51, 83, 123, 145]

Adjust Speed: 2
Adjust Size: 15

Iteration: 0

Current Velocity: 2, 2