Array size and bounds in C++ - Mini Project: Build & Apply

Array size and bounds

📖 Scenario: You are helping a small store keep track of the number of items sold each day in a week. You will use an array to store these numbers.

🎯 Goal: Create an array to hold daily sales for 7 days, set a limit for the array size, and print the sales for each day without going out of bounds.

📋 What You'll Learn

Create an integer array named dailySales with exactly 7 elements.

Create an integer variable named size and set it to 7.

Use a for loop with an index variable i to access each element of dailySales safely.

Print each day's sales using std::cout.

💡 Why This Matters

🌍 Real World

Arrays are used to store lists of data like daily sales, temperatures, or scores. Knowing the size helps avoid errors when reading or writing data.

💼 Career

Understanding array size and bounds is essential for safe programming in many jobs, including software development, data analysis, and embedded systems.

1

Create the array with sales data

Create an integer array called dailySales with these exact values: 5, 8, 6, 7, 9, 4, 3.

C++

// Create the array dailySales with 7 elements
// Your code here

Hint

Use int dailySales[7] = {5, 8, 6, 7, 9, 4, 3}; to create the array.

2

Set the array size variable

Create an integer variable called size and set it to 7.

C++

int dailySales[7] = {5, 8, 6, 7, 9, 4, 3};
// Create the variable size and set it to 7
// Your code here

Hint

Use int size = 7; to store the array size.

3

Loop through the array safely

Use a for loop with the index variable i from 0 to less than size to access each element of dailySales. Inside the loop, write a comment // Access dailySales[i].

C++

int dailySales[7] = {5, 8, 6, 7, 9, 4, 3};
int size = 7;
// Use a for loop with i from 0 to less than size
// Your code here

Hint

Use for (int i = 0; i < size; i++) to loop safely through the array.

4

Print the sales for each day

Inside the for loop, print the text "Day " followed by i + 1, then ": ", and then the value of dailySales[i] using std::cout. After the loop, print a newline.

C++

int dailySales[7] = {5, 8, 6, 7, 9, 4, 3};
int size = 7;
for (int i = 0; i < size; i++) {
    // Print sales for day i+1
    // Your code here
}

Hint

Use std::cout << "Day " << (i + 1) << ": " << dailySales[i] << std::endl; inside the loop.

Practice

1. What is the valid range of indexes for an array declared as int arr[10]; in C++?

easy

A. 1 to 9

B. 1 to 10

C. 0 to 10

D. 0 to 9

Solution

1. Step 1: Understand array size declaration

   The array arr is declared with size 10, meaning it holds 10 elements.

2. Step 2: Determine valid index range

   In C++, array indexing starts at 0, so valid indexes are from 0 up to size-1, which is 9.

3. Final Answer:

   0 to 9 -> Option D

4. Quick Check:

   Array size 10 means indexes 0 to 9 [OK]

Hint: Array indexes start at 0 and end at size minus 1 [OK]

Common Mistakes:

• Thinking indexes start at 1
• Including size as a valid index
• Confusing size with last index

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

easy

A. int arr[5];

B. int arr = 5;

C. int arr(5);

D. int arr{5};

Solution

1. Step 1: Review array declaration syntax

   In C++, arrays are declared using square brackets with the size inside, like int arr[5];.

2. Step 2: Check each option

   int arr(5); uses parentheses which is invalid for arrays. int arr = 5; assigns an int, not an array. int arr{5}; uses brace initialization but without specifying size properly.

3. Final Answer:

   int arr[5]; -> Option A

4. Quick Check:

   Array declaration uses square brackets [OK]

Hint: Use square brackets [] to declare array size [OK]

Common Mistakes:

• Using parentheses instead of brackets
• Assigning a single int instead of array
• Confusing brace initialization with size

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

int arr[3] = {10, 20, 30};
std::cout << arr[3] << std::endl;

medium

A. Undefined behavior (may print garbage or crash)

B. 0

C. 30

D. Compilation error

Solution

1. Step 1: Identify array size and index used

   The array has size 3, valid indexes are 0, 1, 2. The code accesses arr[3], which is out of bounds.

2. Step 2: Understand consequences of out-of-bounds access

   Accessing outside array bounds in C++ causes undefined behavior. It may print garbage, crash, or behave unpredictably.

3. Final Answer:

   Undefined behavior (may print garbage or crash) -> Option A

4. Quick Check:

   Out-of-bounds access causes undefined behavior [OK]

Hint: Access only indexes 0 to size-1 to avoid undefined behavior [OK]

Common Mistakes:

• Assuming arr[3] returns last element
• Expecting zero instead of garbage
• Thinking compiler catches out-of-bounds

4. Identify the error in the following code snippet:

int arr[4] = {1, 2, 3, 4};
for (int i = 0; i <= 4; i++) {
    std::cout << arr[i] << " ";
}

medium

A. Array size should be 5

B. Initialization of array is incorrect

C. Loop condition should be i < 4, not i <= 4

D. No error, code runs fine

Solution

1. Step 1: Analyze loop bounds

   The loop runs from i = 0 to i = 4 inclusive, so it tries to access arr[4].

2. Step 2: Check array size and valid indexes

   Array size is 4, valid indexes are 0 to 3. Accessing arr[4] is out of bounds and causes undefined behavior.

3. Final Answer:

   Loop condition should be i < 4, not i <= 4 -> Option C

4. Quick Check:

   Loop must use i < size to avoid out-of-bounds [OK]

Hint: Use < size, not <= size, in loops over arrays [OK]

Common Mistakes:

• Using <= instead of < in loop condition
• Increasing array size unnecessarily
• Ignoring out-of-bounds access

5. You want to create a function that sums all elements of an integer array passed along with its size. Which of the following function signatures correctly allows safe access to the array elements without causing out-of-bounds errors?

hard

A. int sumArray(int arr[10]);

B. int sumArray(int arr[], int size);

C. int sumArray(int* arr);

D. int sumArray(int arr[]);

Solution

1. Step 1: Understand function parameter requirements

   To safely access array elements, the function must know the array size to avoid out-of-bounds access.

2. Step 2: Evaluate each signature

   int sumArray(int arr[], int size); passes both array and size, allowing safe iteration. int sumArray(int arr[10]); fixes size to 10, which is unsafe if actual size differs. int sumArray(int* arr); passes pointer without size, unsafe. int sumArray(int arr[]); passes array without size, unsafe.

3. Final Answer:

   int sumArray(int arr[], int size); -> Option B

4. Quick Check:

   Pass array and size to avoid out-of-bounds [OK]

Hint: Always pass array size with array to functions [OK]

Common Mistakes:

• Assuming fixed size in function parameter
• Not passing size leads to unsafe access
• Using pointer without size information