Pointers and arrays in C - Mini Project: Build & Apply

Pointers and Arrays in C

📖 Scenario: You are working on a simple program that manages a list of temperatures recorded over a week. You want to use pointers to access and print these temperatures from an array.

🎯 Goal: Build a C program that creates an array of temperatures, uses a pointer to access the array elements, and prints each temperature using the pointer.

📋 What You'll Learn

Create an integer array called temps with exactly 7 values: 23, 25, 22, 20, 24, 26, 21

Create a pointer variable called ptr that points to the first element of temps

Use a for loop with an integer variable i to iterate from 0 to 6

Inside the loop, use the pointer ptr and the index i to access and print each temperature

Print each temperature on its own line using printf

💡 Why This Matters

🌍 Real World

Pointers and arrays are used in many programs to efficiently access and manipulate lists of data, such as sensor readings or user inputs.

💼 Career

Understanding pointers and arrays is essential for C programming jobs, especially in systems programming, embedded development, and performance-critical applications.

1

Create the array of temperatures

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

C

# Create the array temps with 7 temperature values
# Your code here

Hint

Use the syntax int temps[7] = {value1, value2, ..., value7}; to create the array.

2

Create a pointer to the array

Create a pointer variable called ptr that points to the first element of the temps array

C

int temps[7] = {23, 25, 22, 20, 24, 26, 21};
// Create a pointer ptr that points to temps[0]
# Your code here

Hint

Set ptr equal to temps to point to the first element.

3

Use a for loop to access array elements via pointer

Use a for loop with an integer variable i from 0 to 6 to access each temperature using the pointer ptr and the index i

C

int temps[7] = {23, 25, 22, 20, 24, 26, 21};
int *ptr = temps;
// Use a for loop with i from 0 to 6 to access temps via ptr
# Your code here

Hint

Use *(ptr + i) to get the value at index i via the pointer.

4

Print each temperature using the pointer

Inside the for loop, use printf to print each temperature accessed via *(ptr + i) on its own line

C

int temps[7] = {23, 25, 22, 20, 24, 26, 21};
int *ptr = temps;
for (int i = 0; i < 7; i++) {
    int temp = *(ptr + i);
    // Print temp here
# Your code here
}

Hint

Use printf("%d\n", temp); to print each temperature on a new line.

Practice

1. What does a pointer to an array in C typically store?

easy

A. The address of the first element of the array

B. The total number of elements in the array

C. The sum of all elements in the array

D. The value of the last element in the array

Solution

1. Step 1: Understand pointer basics

   A pointer stores a memory address, not values or counts.

2. Step 2: Pointer to array points to first element

   In C, a pointer to an array points to the first element's address.

3. Final Answer:

   The address of the first element of the array -> Option A

4. Quick Check:

   Pointer = first element address [OK]

Hint: Pointers hold addresses, not values or counts [OK]

Common Mistakes:

• Thinking pointer stores array size
• Confusing pointer with array value
• Assuming pointer stores last element

2. Which of the following is the correct way to declare a pointer to an integer array in C?

easy

A. int ptr[];

B. int *ptr;

C. int &ptr;

D. int ptr*;

Solution

1. Step 1: Recall pointer declaration syntax

   In C, a pointer to int is declared as int *ptr;

2. Step 2: Check other options for syntax errors

   int ptr[] declares an array, not a pointer; int &ptr is invalid in C; int ptr* is incorrect syntax.

3. Final Answer:

   int *ptr; -> Option B

4. Quick Check:

   Pointer syntax uses * before variable [OK]

Hint: Pointer declaration uses * before variable name [OK]

Common Mistakes:

• Using array syntax instead of pointer
• Confusing C++ reference (&) with pointer
• Placing * after variable name incorrectly

3. What is the output of the following C code?

int arr[] = {10, 20, 30};
int *p = arr;
printf("%d", *(p + 1));

medium

A. 10

B. 30

C. Garbage value

D. 20

Solution

1. Step 1: Understand pointer arithmetic

   p points to arr[0], so p + 1 points to arr[1].

2. Step 2: Dereference pointer at p + 1

   *(p + 1) gives value at arr[1], which is 20.

3. Final Answer:

   20 -> Option D

4. Quick Check:

   *(p+1) = arr[1] = 20 [OK]

Hint: Pointer + 1 moves to next array element [OK]

Common Mistakes:

• Confusing *(p+1) with *p
• Assuming pointer arithmetic adds 1 byte
• Expecting arr[0] value instead

4. Identify the error in this C code snippet:

int arr[3] = {1, 2, 3};
int *p = arr + 3;
printf("%d", *p);

medium

A. Missing semicolon after array declaration

B. Array size is incorrect

C. Pointer points outside array bounds causing undefined behavior

D. Pointer declaration syntax is wrong

Solution

1. Step 1: Analyze pointer assignment

   arr + 3 points one element past the last array element (out of bounds).

2. Step 2: Dereferencing out-of-bounds pointer

   *p accesses invalid memory, causing undefined behavior.

3. Final Answer:

   Pointer points outside array bounds causing undefined behavior -> Option C

4. Quick Check:

   Pointer out of array range = error [OK]

Hint: Pointer must stay within array limits [OK]

Common Mistakes:

• Ignoring pointer out-of-bounds access
• Thinking array size is wrong
• Confusing pointer syntax errors

5. Given the code below, what will be printed?

int arr[] = {5, 10, 15, 20};
int *p = arr;
for(int i = 0; i < 4; i++) {
    printf("%d ", *(p + i));
}

hard

A. 5 10 15 20

B. 20 15 10 5

C. 5 5 5 5

D. Compilation error

Solution

1. Step 1: Understand the loop and pointer arithmetic

   Loop runs i from 0 to 3, *(p + i) accesses arr[i].

2. Step 2: Print each element in order

   Values printed are arr[0]=5, arr[1]=10, arr[2]=15, arr[3]=20.

3. Final Answer:

   5 10 15 20 -> Option A

4. Quick Check:

   Pointer + i accesses arr[i] in order [OK]

Hint: Pointer + i accesses array element i [OK]

Common Mistakes:

• Assuming reverse order print
• Printing same element repeatedly
• Expecting syntax error