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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.
public class Main {
public static void main(String[] args) {
// The target numbers
int[] list = {0, 4, 51, 83, 92, 10, 123, 145};
// Creating empty arraylist for the even and odd numbers
ArrayList<Integer> evenList = new ArrayList<>();
ArrayList<Integer> oddList = new ArrayList<>();
// Using the for loop here...
System.out.println("Using for loop:");
for (int i = 0; i < list.length; i++) {
System.out.println(list[i]); // Print the current element
if (list[i] % 2 == 0) {
evenList.add(list[i]); // Add to even list if the number is even
} else {
oddList.add(list[i]); // Add to odd list if the number is odd
}
}
// Using the for-each loop here...
System.out.println("\nUsing for-each loop:");
for (int item : list) {
System.out.println(item); // Print each element of the list
}
// Printing out the even and odd numbers here
System.out.println("\nEven numbers: " + evenList);
System.out.println("Odd numbers: " + oddList);
}
}
Main.main(null);
Using 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]
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15
15
Iteration: 0
Current Velocity: 2, 2