The problem this code solves

A fitness app stores every daily step count for a user in an array. To show the weekly summary, the app has to walk the array and compute things: the total steps, how many days hit the goal, the best day, and the average. None of these are built in. Each is a loop that visits every element and carries a value forward. That carry-forward value is the heart of every loop algorithm, and it is exactly the skill FRQ 1 tests.

One loop shape, four carried values

Every algorithm below is the same for-loop over the array. What changes is the variable you carry and how you update it. Read the Java on the left and the memory trace on the right together.

1. Accumulator (running total)

int[] data = {4, 8, 15};
int sum = 0;          // start empty
for (int i = 0; i < data.length; i++) {
    sum += data[i];   // carry forward
}
System.out.println(sum);

The accumulator starts at the identity value (0 for a sum) and each pass folds one element in. A count is the same shape with += 1 instead of += data[i].

2. Counter with a condition

int count = 0;
for (int i = 0; i < data.length; i++) {
    if (data[i] % 2 == 0) {
        count++;      // only when even
    }
}

3. Maximum (or minimum)

int max = data[0];   // NOT 0
for (int i = 1; i < data.length; i++) {
    if (data[i] > max) {
        max = data[i];
    }
}

4. Average (the integer-division trap)

int sum = 108;
int n = 6;
// WRONG: int / int truncates
double bad = sum / n;        // 18.0? no
// RIGHT: cast first
double avg = (double) sum / n;

Vocabulary

Predict first, then check

Live code editor

Eight problems, six scaffolded and two open-ended. Write Java, press Run to execute it, and Check to test against the expected output. Hints and the solution are here if you need them, but using them is tracked, so try first.

Accumulator Arcade

Six quick rounds. Read the array and the operation, then type the value the loop would carry out. Speed and accuracy build the pattern recognition the timed exam rewards.

Multiple choice

Predict your answer before reading the options. Watch for the qualifier words. After you answer, the rationale explains every distractor.

FRQ 1 connection: Methods and Control Structures

FRQ 1 always asks you to implement a method using a loop and a conditional. This is that skill in miniature: combine a counter or accumulator with an if. Write it, run it, and check it the same way you did in the editor.

Choose your lane