Common array operations in C++ - Mini Project: Build & Apply

Common array operations

📖 Scenario: You are working with a list of daily temperatures recorded over a week. You want to perform some common operations on this list to understand the data better.

🎯 Goal: Build a simple C++ program that stores daily temperatures in an array, calculates the average temperature, finds the highest temperature, and prints the results.

📋 What You'll Learn

Create an array with exactly 7 integer temperature values

Create a variable to hold the sum of temperatures

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

Calculate the average temperature as a float

Find the highest temperature using a variable maxTemp

Print the average and highest temperature exactly as shown

💡 Why This Matters

🌍 Real World

Arrays are used to store collections of data like temperatures, sales numbers, or scores. Knowing how to process arrays helps analyze and summarize data.

💼 Career

Many programming jobs require working with arrays and loops to handle lists of information efficiently.

1

Create the temperature array

Create an integer array called temperatures with these exact values: 23, 25, 20, 22, 24, 26, 21

C++

# Create the array temperatures with 7 values
// Your code here

Hint

Use the syntax int arrayName[size] = {values}; to create the array.

2

Set up sum and max variables

Create an integer variable sum and set it to 0. Create an integer variable maxTemp and set it to the first element of temperatures.

C++

int temperatures[7] = {23, 25, 20, 22, 24, 26, 21};
// Create sum and maxTemp variables
// Your code here

Hint

Initialize sum to 0 and maxTemp to the first temperature value.

3

Calculate sum and find max temperature

Use a for loop with index variable i from 0 to 6 to add each temperature to sum. Inside the loop, update maxTemp if temperatures[i] is greater than maxTemp.

C++

int temperatures[7] = {23, 25, 20, 22, 24, 26, 21};
int sum = 0;
int maxTemp = temperatures[0];
// Use a for loop to sum and find max temperature
// Your code here

Hint

Loop from 0 to 6, add each temperature to sum, and update maxTemp if needed.

4

Calculate average and print results

Create a float variable average and set it to sum divided by 7.0. Then print the average temperature with the text "Average temperature: " and the highest temperature with the text "Highest temperature: ".

C++

int temperatures[7] = {23, 25, 20, 22, 24, 26, 21};
int sum = 0;
int maxTemp = temperatures[0];
for (int i = 0; i  maxTemp) {
        maxTemp = temperatures[i];
    }
}
// Calculate average and print results
// Your code here

Hint

Divide sum by 7.0 to get a float average. Use std::cout to print the results.

Practice

1. What does the following C++ code do?
int arr[5] = {1, 2, 3, 4, 5};

easy

A. Creates an array of 5 integers with values 1 to 5

B. Creates a vector of 5 integers with values 1 to 5

C. Creates a pointer to an integer array

D. Declares an uninitialized array of size 5

Solution

1. Step 1: Understand array declaration

   The code declares an integer array named arr with size 5.

2. Step 2: Check initialization

   The array is initialized with values 1, 2, 3, 4, 5 in order.

3. Final Answer:

   Creates an array of 5 integers with values 1 to 5 -> Option A

4. Quick Check:

   Array declaration with initialization = Creates array with values [OK]

Hint: Array size and values in braces means initialized array [OK]

Common Mistakes:

• Confusing array with vector
• Thinking it's a pointer declaration
• Assuming array is uninitialized

2. Which of the following is the correct syntax to access the third element of an array named arr in C++?

easy

A. arr[3];

B. arr(3);

C. arr{3};

D. arr[2];

Solution

1. Step 1: Recall zero-based indexing

   Arrays in C++ start at index 0, so the third element is at index 2.

2. Step 2: Identify correct syntax for access

   Array elements are accessed using square brackets, so arr[2] is correct.

3. Final Answer:

   arr[2]; -> Option D

4. Quick Check:

   Third element index = 2, use square brackets [OK]

Hint: Remember arrays start at 0, so third element is index 2 [OK]

Common Mistakes:

• Using parentheses instead of brackets
• Using 1-based indexing
• Using curly braces for access

3. What is the output of this C++ code?

int arr[4] = {10, 20, 30, 40};
int sum = 0;
for(int i = 0; i < 4; i++) {
    sum += arr[i];
}
std::cout << sum;

medium

A. 100

B. 90

C. 40

D. 10

Solution

1. Step 1: Identify array elements and loop

   The array has elements 10, 20, 30, 40 and the loop runs from i=0 to 3.

2. Step 2: Calculate sum of elements

   sum = 10 + 20 + 30 + 40 = 100

3. Final Answer:

   100 -> Option A

4. Quick Check:

   Sum of all elements = 100 [OK]

Hint: Add all elements in loop to get sum [OK]

Common Mistakes:

• Stopping loop early
• Using wrong indices
• Printing sum before loop

4. Find the error in this C++ code that tries to print all elements of an array:

int arr[3] = {5, 10, 15};
for(int i = 1; i <= 3; i++) {
    std::cout << arr[i] << " ";
}

medium

A. Loop index starts at 1 instead of 0

B. Array size is incorrect

C. Using <= causes out-of-bounds access

D. Missing semicolon after cout statement

Solution

1. Step 1: Analyze loop indices

   The loop runs i from 1 to 3 inclusive, so i=3 is included.

2. Step 2: Check array bounds

   Array indices are 0,1,2. Accessing arr[3] is out-of-bounds and causes error.

3. Final Answer:

   Using <= causes out-of-bounds access -> Option C

4. Quick Check:

   Loop must use i < size, not <= [OK]

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

Common Mistakes:

• Starting loop at 1 instead of 0 (not error but unusual)
• Ignoring out-of-bounds access
• Assuming array size is wrong

5. You have an array int arr[6] = {2, 4, 6, 8, 10, 12};. How do you update the element with value 8 to 9 using a loop?

hard

A. arr[3] = 9;

B. for(int i=0; i<6; i++) { if(arr[i] == 8) arr[i] = 9; }

C. for(int i=1; i<=6; i++) { if(arr[i] == 8) arr[i] = 9; }

D. arr[4] = 9;

Solution

1. Step 1: Understand the problem

   We want to find the element with value 8 and update it to 9 using a loop.

2. Step 2: Check loop and condition

   Loop from i=0 to 5 checks each element; if arr[i] == 8, assign arr[i] = 9.

3. Final Answer:

   for(int i=0; i<6; i++) { if(arr[i] == 8) arr[i] = 9; } -> Option B

4. Quick Check:

   Loop with condition to find and update element [OK]

Hint: Loop through array, check value, then update [OK]

Common Mistakes:

• Using wrong indices in loop
• Assigning wrong array index
• Not using loop to find value