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)

|   #python version

illegal character: '#'



|   array=[1, 2, 3, 4, 5]

illegal start of expression

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.

int[] int_list = {0, 4, 51, 83, 92, 10, 123, 145};
int[] evens = new int[int_list.length]; // Temporary array for evens
int[] odds = new int[int_list.length];  // Temporary array for odds
int evenCount = 0; // Counter for even elements
int oddCount = 0;  // Counter for odd elements

// Using a single loop
for (int i = 0; i < int_list.length; i++) {
    if (int_list[i] % 2 == 0) { // Check if the item is even
        evens[evenCount] = int_list[i]; // Add to evens array
        evenCount++; // Increment the even counter
    } else {
        odds[oddCount] = int_list[i]; // Add to odds array
        oddCount++; // Increment the odd counter
    }
}

// Print the even numbers
System.out.print("Even numbers: ");
for (int i = 0; i < evenCount; i++) {
    System.out.print(evens[i] + " ");
}
System.out.println(); // New line for better formatting

// Print the odd numbers
System.out.print("Odd numbers: ");
for (int i = 0; i < oddCount; i++) {
    System.out.print(odds[i] + " ");
}

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

Adjust Speed: 2
Adjust Size: 15

Iteration: 0

Current Velocity: 2, 2