Common array operations - 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 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 integer array with exactly 7 elements representing daily temperatures.

Create an integer variable to hold the sum of temperatures.

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

Calculate the average temperature as a float.

Find the highest temperature using a variable called max_temp.

Print the average temperature and the highest temperature using printf.

💡 Why This Matters

🌍 Real World

Analyzing temperature data helps in weather forecasting and understanding climate patterns.

💼 Career

Knowing how to work with arrays and loops is essential for many programming jobs, especially in data processing and embedded systems.

1

Create the temperature array

Create an integer array called temperatures with exactly 7 elements: 23, 25, 19, 22, 24, 20, 21.

C

# Create the integer array temperatures with 7 elements
// Your code here

Hint

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

2

Create a sum variable

Create an integer variable called sum and set it to 0 to hold the total of temperatures.

C

int temperatures[7] = {23, 25, 19, 22, 24, 20, 21};
// Create an integer variable sum and set it to 0
// Your code here

Hint

Initialize sum to zero before adding temperatures.

3

Calculate the sum and find the max temperature

Use a for loop with the variable i from 0 to 6 to add each element of temperatures to sum. Also, create an integer variable max_temp initialized to the first element of temperatures. Inside the loop, update max_temp if the current temperature is higher.

C

int temperatures[7] = {23, 25, 19, 22, 24, 20, 21};
int sum = 0;
// Create max_temp and set it to temperatures[0]
// Use a for loop with i from 0 to 6 to add temperatures[i] to sum
// Inside the loop, update max_temp if temperatures[i] is greater
// Your code here

Hint

Use for (int i = 0; i < 7; i++) to loop through the array.

4

Calculate average and print results

Create a float variable called average and set it to sum / 7.0f. Then use printf to print the average temperature with one decimal place and the highest temperature as an integer.

C

int temperatures[7] = {23, 25, 19, 22, 24, 20, 21};
int sum = 0;
int max_temp = temperatures[0];
for (int i = 0; i  max_temp) {
        max_temp = temperatures[i];
    }
}
// Calculate average as float
// Print average and max_temp using printf
// Your code here

Hint

Use float average = sum / 7.0f; to get a decimal average.

Use printf("Average temperature: %.1f\n", average); to print one decimal place.

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 pointer to an integer

C. Declares a single integer variable

D. Creates a 2D array of integers

Solution

1. Step 1: Understand the declaration

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

2. Step 2: Check the initialization

   The array is initialized with values 1, 2, 3, 4, and 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 an array of 5 integers with values 1 to 5 [OK]

Hint: Array size and values match initialization count [OK]

Common Mistakes:

• Confusing array with pointer declaration
• Thinking it's a single variable, not an array
• Assuming it's a 2D array

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

easy

A. arr(3)

B. arr[2]

C. arr{3}

D. arr[3]

Solution

1. Step 1: Recall array indexing in C

   Arrays in C use zero-based indexing, so the first element is arr[0].

2. Step 2: Identify the third element index

   The third element is at index 2, so arr[2] accesses it.

3. Final Answer:

   arr[2] -> Option B

4. Quick Check:

   Third element index = 2 [OK]

Hint: Remember C arrays start at index 0 [OK]

Common Mistakes:

• Using parentheses instead of brackets
• Using 1-based indexing (arr[3])
• 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];
}
printf("%d", sum);

medium

A. 100

B. 90

C. Syntax error

D. 40

Solution

1. Step 1: Sum all elements in the array

   The loop adds arr[0]=10, arr[1]=20, arr[2]=30, arr[3]=40 to sum.

2. Step 2: Calculate the total sum

   10 + 20 + 30 + 40 = 100.

3. Final Answer:

   100 -> Option A

4. Quick Check:

   Sum of array elements = 100 [OK]

Hint: Add all elements using loop index 0 to size-1 [OK]

Common Mistakes:

• Off-by-one error in loop causing wrong sum
• Confusing sum with last element value
• Syntax errors from missing semicolons

4. Identify the error in this code snippet:

int arr[3] = {1, 2, 3};
for(int i = 0; i <= 3; i++) {
    printf("%d ", arr[i]);
}

medium

A. Array size should be 4

B. printf format specifier is wrong

C. Loop condition should be i < 3, not i <= 3

D. Variable i should be declared outside the loop

Solution

1. Step 1: Analyze loop condition

   The loop runs from i=0 to i=3 inclusive, so it accesses arr[3].

2. Step 2: Check array bounds

   Array arr has size 3, valid indices are 0,1,2. Accessing arr[3] causes out-of-bounds error.

3. Final Answer:

   Loop condition should be i < 3, not i <= 3 -> Option C

4. Quick Check:

   Array index must be less than size [OK]

Hint: Loop index must be less than array size [OK]

Common Mistakes:

• Using <= instead of < in loop condition
• Assuming array size auto-expands
• Misunderstanding printf format specifier

5. You want to find the largest number in an integer array arr of size n. Which code snippet correctly does this?

hard

A. int max = arr[n]; for(int i = 0; i < n; i++) { if(arr[i] > max) max = arr[i]; }

B. int max = 0; for(int i = 0; i <= n; i++) { if(arr[i] > max) max = arr[i]; }

C. int max = arr[0]; for(int i = 1; i < n; i++) { if(arr[i] < max) max = arr[i]; }

D. int max = arr[0]; for(int i = 1; i < n; i++) { if(arr[i] > max) max = arr[i]; }

Solution

1. Step 1: Initialize max with first element

   Set max = arr[0] to start comparison from first element.

2. Step 2: Loop from second element to end

   Loop i from 1 to n-1, compare arr[i] with max, update max if arr[i] is larger.

3. Step 3: Check other options for errors

   int max = 0; for(int i = 0; i <= n; i++) { if(arr[i] > max) max = arr[i]; } uses max=0 which fails if all numbers are negative; loop condition i <= n causes out-of-bounds; int max = arr[n]; for(int i = 0; i < n; i++) { if(arr[i] > max) max = arr[i]; } initializes max with arr[n] which is invalid index; int max = arr[0]; for(int i = 1; i < n; i++) { if(arr[i] < max) max = arr[i]; } finds minimum instead of maximum.

4. Final Answer:

   int max = arr[0]; for(int i = 1; i < n; i++) { if(arr[i] > max) max = arr[i]; } -> Option D

5. Quick Check:

   Initialize max with first element and compare correctly [OK]

Hint: Start max with arr[0], loop i from 1 to n-1 [OK]

Common Mistakes:

• Using wrong loop bounds causing out-of-bounds access
• Initializing max with 0 ignoring negative values
• Confusing max with min logic