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);
}

0
1
2
3
4

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
}

0
1
2
3
4

#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;


int[] list = {0, 4, 51, 83, 92, 10, 123, 145};
ArrayList<Integer> odd = new ArrayList<>();
ArrayList<Integer> even = new ArrayList<>();

for (int i = 0; i < list.length; i++) {
    if (list[i] % 2 == 0) {
        even.add(list[i]);
    } else {
        odd.add(list[i]);
    }
}

System.out.println("Odd:");
for (int item : odd) {
    System.out.println(item);
}

System.out.println("Even:");
for (int item : even) {
    System.out.println(item);
}

Odd:
51
83
123
145
Even:
0
4
92
10

Adjust Speed: 2
Adjust Size: 15

Iteration: 0

Current Velocity: 2, 2