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.

int[] int_list = {0,4,51,83,92,10,123,145};
System.out.println("for");
for(int i = 0; i < int_list.length; i++) {
    System.out.println(int_list[i]);
}
System.out.println("foreach");
for (int value : int_list) {
    System.out.println(value);
}
int evenCount;
int oddCount;
for(int i = 0; i < int_list.length; i++) {
    if (int_list[i] % 2 == 0) {
        evenCount++;
    }

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

System.out.println("even " + Arrays.toString(even) + " odd " + Arrays.toString(odd));

for


0
4
51
83
92
10
123
145
foreach
0
4
51
83
92
10
123
145
even [0, 4, 92, 10] odd [51, 83, 123, 145]
2
15


Iteration: 0

Current Velocity: 2, 2