One-dimensional arrays in C++ - Mini Project: Build & Apply

Working with One-Dimensional Arrays in C++

📖 Scenario: You are helping a small store keep track of the prices of five products. You will use a one-dimensional array to store these prices and then calculate the total cost.

🎯 Goal: Create a program that stores product prices in an array, calculates the total price, and prints the total.

📋 What You'll Learn

Create a one-dimensional array called prices with exactly five double values: 10.5, 23.0, 7.25, 15.0, and 9.99

Create a variable called total of type double and initialize it to 0

Use a for loop with the variable i to iterate over the prices array

Add each price to the total inside the loop

Print the total with the message Total price:

💡 Why This Matters

🌍 Real World

Stores and shops often use arrays to keep track of product prices or quantities.

💼 Career

Understanding arrays and loops is essential for programming tasks like data processing, inventory management, and financial calculations.

1

Create the prices array

Create a one-dimensional array called prices of type double with these exact values: 10.5, 23.0, 7.25, 15.0, and 9.99.

C++

// Your code here

Hint

Use the syntax double prices[5] = {value1, value2, ..., value5}; to create the array.

2

Create the total variable

Create a variable called total of type double and set it to 0 inside the main function, after the prices array.

C++

#include 

int main() {
    double prices[5] = {10.5, 23.0, 7.25, 15.0, 9.99};
    
    // Create total variable here
    
    return 0;
}

Hint

Write double total = 0; inside the main function.

3

Calculate the total price using a for loop

Use a for loop with the variable i to iterate from 0 to 4 (inclusive). Inside the loop, add prices[i] to the total variable.

C++

#include 

int main() {
    double prices[5] = {10.5, 23.0, 7.25, 15.0, 9.99};
    double total = 0;
    
    // Add a for loop to sum prices
    
    return 0;
}

Hint

Use for (int i = 0; i < 5; i++) and inside the loop write total += prices[i];.

4

Print the total price

Write a std::cout statement to print the text Total price: followed by the value of total. Then add a newline.

C++

#include 

int main() {
    double prices[5] = {10.5, 23.0, 7.25, 15.0, 9.99};
    double total = 0;
    for (int i = 0; i < 5; i++) {
        total += prices[i];
    }
    
    // Print total price
    
    return 0;
}

Hint

Use std::cout << "Total price: " << total << std::endl; to print.

Practice

1. What is the starting index of a one-dimensional array in C++?

easy

A. -1

B. 1

C. 0

D. Depends on the array size

Solution

1. Step 1: Understand array indexing in C++

   Arrays in C++ always start indexing from 0, meaning the first element is at index 0.

2. Step 2: Confirm the index range

   Indexes go from 0 up to size-1, so the first index is always 0 regardless of array size.

3. Final Answer:

   0 -> Option C

4. Quick Check:

   Array indexing starts at 0 [OK]

Hint: Remember: C++ arrays always start at zero index [OK]

Common Mistakes:

• Thinking arrays start at 1
• Assuming negative indexes are valid
• Confusing with other languages

2. Which of the following is the correct way to declare an integer array of size 5 in C++?

easy

A. array<int> arr(5);

B. int arr(5);

C. int arr = new int[5];

D. int arr[5];

Solution

1. Step 1: Recall C++ array declaration syntax

   In C++, a fixed-size array is declared using square brackets with size: int arr[5];

2. Step 2: Check other options for correctness

   int arr(5); uses parentheses which is invalid for arrays. array<int> arr(5); uses incorrect syntax (not standard array). int arr = new int[5]; uses dynamic allocation syntax but is incorrect without pointer.

3. Final Answer:

   int arr[5]; -> Option D

4. Quick Check:

   Fixed-size arrays use square brackets [OK]

Hint: Use square brackets [] to declare fixed-size arrays [OK]

Common Mistakes:

• Using parentheses instead of brackets
• Confusing with vector syntax
• Incorrect dynamic allocation syntax

3. What will be the output of the following code?

int arr[4] = {10, 20, 30, 40};
std::cout << arr[2];

medium

A. 30

B. 20

C. 40

D. Compilation error

Solution

1. Step 1: Identify the array elements and indexes

   The array arr has elements: arr[0]=10, arr[1]=20, arr[2]=30, arr[3]=40.

2. Step 2: Access the element at index 2

   arr[2] is 30, so std::cout will print 30.

3. Final Answer:

   30 -> Option A

4. Quick Check:

   arr[2] = 30 [OK]

Hint: Remember array index starts at 0, so arr[2] is third element [OK]

Common Mistakes:

• Confusing index 2 with 1 or 3
• Expecting output 20 or 40
• Thinking code causes error

4. Identify the error in the following code snippet:

int arr[3] = {1, 2, 3};
for(int i = 0; i <= 3; i++) {
    std::cout << arr[i] << " ";
}

medium

A. Missing semicolon after array declaration

B. Loop runs one time too many, causing out-of-bounds access

C. Syntax error in for loop declaration

D. Array size is incorrect, should be 4

Solution

1. Step 1: Analyze the loop range and array size

   The array has size 3 with valid indexes 0,1,2. The loop runs from i=0 to i=3 inclusive, which means 4 iterations.

2. Step 2: Identify out-of-bounds access

   When i=3, arr[3] is accessed, which is outside the array bounds and causes undefined behavior.

3. Final Answer:

   Loop runs one time too many, causing out-of-bounds access -> Option B

4. Quick Check:

   Loop index must be less than array size [OK]

Hint: Loop index must be less than array size, not less or equal [OK]

Common Mistakes:

• Using <= instead of <
• Assuming array size is 4
• Ignoring out-of-bounds errors

5. Given an integer array arr of size n, which code snippet correctly calculates the sum of all elements?

hard

A. int sum = 0;
for(int i = 0; i < n; i++) sum += arr[i];

B. int sum = 0;
for(int i = 1; i < n; i++) sum += arr[i];

C. int sum = 0;
for(int i = 0; i <= n; i++) sum += arr[i];

D. int sum = arr[0];
for(int i = 1; i < n; i++) sum = arr[i];

Solution

1. Step 1: Understand correct loop bounds for array traversal

   Array indexes go from 0 to n-1, so loop must run i from 0 to less than n.

2. Step 2: Check each option for correctness

   int sum = 0; for(int i = 1; i < n; i++) sum += arr[i]; starts from 1, missing arr[0]. int sum = 0; for(int i = 0; i <= n; i++) sum += arr[i]; uses <= n, causing out-of-bounds access. int sum = 0; for(int i = 0; i < n; i++) sum += arr[i]; correctly sums all elements from 0 to n-1. int sum = arr[0]; for(int i = 1; i < n; i++) sum = arr[i]; overwrites sum instead of adding.

3. Final Answer:

   int sum = 0; for(int i = 0; i < n; i++) sum += arr[i]; -> Option A

4. Quick Check:

   Loop from 0 to n-1 sums all elements [OK]

Hint: Loop from 0 to less than n to cover all elements [OK]

Common Mistakes:

• Starting loop at 1
• Using <= n causing errors
• Overwriting sum instead of adding