Build a shopping total

1 min read

You have run your first program. Now combine variables, lists, loops, and functions into a small project. This program adds item prices and reports whether they fit your budget.

Create the project

dreamer init shopping
cd shopping

Replace src/main.dream with:

import system;
import system.collections;

fun total(borrow prices: List<int>): int {
    let sum = 0;
    for (let price in prices) {
        sum = sum + price;
    }
    return sum;
}

fun main() {
    let prices: List<int> = [12, 8, 5];
    prices.push(10);
    const budget = 40;
    let cost = total(prices);
    System.println(cost);
    if cost <= budget {
        System.println("Within budget");
    } else {
        System.println("Over budget");
    }
}

Run dreamer run. You should see:

35
Within budget

Understand each part

List<int> holds whole-number prices. push(10) adds another price. The function receives the list through a borrowed parameter, visits its items, and returns their sum. const budget keeps the budget fixed. The if statement chooses which message to print.

The prices are whole numbers to keep this example small. For money that includes fractions, store the smallest currency unit as an integer; for example, store 125 cents rather than 1.25 dollars.

Try a change

Set the budget to 30 and run again. The total stays 35, but the message becomes Over budget. Add another price and check that the total changes.

Add a test

Create tests/total.dream:

import system.testing;

@test
fun four_prices(): void {
    Assert.eq(12 + 8 + 5 + 10, 35);
}

Run dreamer test. This first test checks the example's arithmetic. As your project grows, put reusable functions in their own module and test those functions directly.

Continue with Lists, Functions, or project testing.