Loop execution flow in Javascript - Mini Project: Build & Apply

Loop Execution Flow

📖 Scenario: You are helping a small shop owner keep track of daily sales. Each day, the shop records the number of items sold. You want to calculate the total items sold over a week.

🎯 Goal: Build a program that uses a for loop to add up daily sales and show the total items sold in the week.

📋 What You'll Learn

Create an array with daily sales numbers for 7 days

Create a variable to hold the total sales starting at 0

Use a for loop to add each day's sales to the total

Print the total sales after the loop finishes

💡 Why This Matters

🌍 Real World

Shops and businesses often need to add up daily sales or counts to understand their performance over time.

💼 Career

Knowing how to use loops to process lists of data is a key skill for many programming jobs, especially in data processing and automation.

1

Create the daily sales data

Create an array called dailySales with these exact numbers: 5, 8, 6, 7, 4, 9, 3 representing sales for each day of the week.

Javascript

// Create the dailySales array with the given numbers
// Your code here

Hint

Use square brackets [] to create an array and separate numbers with commas.

2

Set up the total sales counter

Create a variable called totalSales and set it to 0 to start counting total items sold.

Javascript

const dailySales = [5, 8, 6, 7, 4, 9, 3];
// Create totalSales variable and set it to 0
// Your code here

Hint

Use let to create a variable that can change later.

3

Add daily sales using a for loop

Use a for loop with a variable i starting at 0 and running while i < dailySales.length. Inside the loop, add dailySales[i] to totalSales.

Javascript

const dailySales = [5, 8, 6, 7, 4, 9, 3];
let totalSales = 0;
// Write a for loop to add each daily sale to totalSales
// Your code here

Hint

Remember to use i++ to increase the counter each time.

4

Display the total sales

Write console.log(totalSales) to print the total items sold after the loop.

Javascript

const dailySales = [5, 8, 6, 7, 4, 9, 3];
let totalSales = 0;
for (let i = 0; i < dailySales.length; i++) {
    totalSales += dailySales[i];
}
// Print the totalSales value
// Your code here

Hint

The total should be the sum of all numbers in the array.

Practice

1. What does a for loop do in JavaScript?

easy

A. Stops the program immediately

B. Runs code only once

C. Creates a new variable

D. Repeats code a set number of times

Solution

1. Step 1: Understand the purpose of a for loop

   A for loop is designed to repeat code multiple times based on a condition.

2. Step 2: Identify the correct description

   Among the options, only repeating code a set number of times matches the for loop behavior.

3. Final Answer:

   Repeats code a set number of times -> Option D

4. Quick Check:

   for loop = repeat fixed times [OK]

Hint: For loops repeat code a fixed number of times [OK]

Common Mistakes:

• Thinking for loops run only once
• Confusing for loops with if statements
• Believing for loops stop the program

2. Which of the following is the correct syntax for a for loop in JavaScript?

easy

A. for i = 0 to 5 { }

B. for (let i = 0; i < 5; i++) { }

C. loop (i = 0; i < 5; i++) { }

D. for (i < 5; i = 0; i++) { }

Solution

1. Step 1: Recall JavaScript for loop syntax

   The correct syntax uses for (initialization; condition; increment) { }.

2. Step 2: Compare options to syntax

   Only for (let i = 0; i < 5; i++) { } matches the correct syntax with let i = 0; i < 5; i++.

3. Final Answer:

   for (let i = 0; i < 5; i++) { } -> Option B

4. Quick Check:

   for loop syntax = initialization; condition; increment [OK]

Hint: Remember for loop uses three parts inside parentheses [OK]

Common Mistakes:

• Using incorrect keywords like 'loop'
• Swapping initialization and condition
• Missing semicolons inside for parentheses

3. What will be the output of this code?

let sum = 0;
for (let i = 1; i <= 3; i++) {
  sum += i;
}
console.log(sum);

medium

A. 6

B. 3

C. 0

D. Error

Solution

1. Step 1: Trace the loop iterations

   The loop runs with i = 1, 2, 3. Each time, sum adds i: 0+1=1, 1+2=3, 3+3=6.

2. Step 2: Determine final sum value

   After the loop, sum is 6, which is printed by console.log.

3. Final Answer:

   6 -> Option A

4. Quick Check:

   Sum 1+2+3 = 6 [OK]

Hint: Add numbers step-by-step inside the loop [OK]

Common Mistakes:

• Stopping loop early
• Adding wrong values
• Confusing sum initialization

4. Find the error in this loop:

for (let i = 0; i < 5; i--) {
  console.log(i);
}

medium

A. Console.log is incorrect

B. Syntax error in for loop

C. The loop will run infinitely because i decreases

D. Variable i is not declared

Solution

1. Step 1: Analyze the loop increment/decrement

   The loop uses i--, so i decreases each time starting from 0.

2. Step 2: Check loop condition

   The condition is i < 5, which is true for all i less than 5, including negative numbers. Since i decreases, it never reaches 5 or more, so loop never ends.

3. Final Answer:

   The loop will run infinitely because i decreases -> Option C

4. Quick Check:

   Decrement with < condition causes infinite loop [OK]

Hint: Check if increment matches loop condition direction [OK]

Common Mistakes:

• Confusing i-- with i++
• Ignoring loop condition logic
• Assuming loop stops automatically

5. How many times will this loop run?

let count = 0;
let i = 10;
while (i > 0) {
  i -= 3;
  count++;
}
console.log(count);

hard

A. 4

B. 3

C. 5

D. 6

Solution

1. Step 1: Trace the while loop iterations

   Start i=10, count=0. Each loop: i decreases by 3, count increases by 1.
   Iterations:
   1) i=7, count=1
   2) i=4, count=2
   3) i=1, count=3
   4) i=-2, count=4 (loop stops after this because i > 0 is false)

2. Step 2: Count total iterations

   The loop runs 4 times before i becomes -2 and condition fails.

3. Final Answer:

   4 -> Option A

4. Quick Check:

   Subtract 3 until i ≤ 0 counts 4 times [OK]

Hint: Count how many times i decreases by 3 until ≤ 0 [OK]

Common Mistakes:

• Counting one less or more iteration
• Not updating count correctly
• Misunderstanding while loop condition