Lab: Pointers

1. Program: Pointer Basics

#include <stdio.h>

int main() {
    int num = 25;         
    int *ptr;             

    ptr = &num;           

    printf("Value of num using pointer: %d\n", *ptr);
    printf("Address of num using pointer: %p\n", ptr);
    printf("Address of num directly: %p\n", &num);

    return 0;
}

Explanation:

• int *ptr: Declares a pointer ptr that can hold the address of an integer variable.
• ptr = &num: Assigns the address of the variable num to the pointer ptr.
• *ptr: Dereferences the pointer to access the value stored at the memory location ptr is pointing to.
• ptr: Directly prints the memory address stored in the pointer.

Sample Output:

Value of num using pointer: 25
Address of num using pointer: 0x7ffee4f2b98c
Address of num directly: 0x7ffee4f2b98c

2. Program: Sum of Two Numbers Using Pointers

#include <stdio.h>

int main() {
    int num1, num2, sum;
    int *ptr1, *ptr2;  

    // Input two numbers
    printf("Enter the first number: ");
    scanf("%d", &num1);
    printf("Enter the second number: ");
    scanf("%d", &num2);

    // Assign the addresses of num1 and num2 to the pointers
    ptr1 = &num1;
    ptr2 = &num2;

    // Calculate the sum using pointers
    sum = *ptr1 + *ptr2;

    // Print the result
    printf("The sum of %d and %d is: %d\n", *ptr1, *ptr2, sum);

    return 0;
}

Explanation:

• int *ptr1, *ptr2: Declares two pointers ptr1 and ptr2 to store the addresses of the integers num1 and num2.
• ptr1 = &num1 and ptr2 = &num2: Assign the addresses of num1 and num2 to the pointers.
• sum = *ptr1 + *ptr2: Dereferences the pointers to get the values of num1 and num2, adds them together, and stores the result in sum.

Sample Output:

Enter the first number: 10
Enter the second number: 20
The sum of 10 and 20 is: 30

3. Program: Largest of Three Numbers Using Pointers

#include <stdio.h>

int main() {
    int num1, num2, num3;
    int *ptr1, *ptr2, *ptr3;  
    int *largest;             

    // Input three numbers
    printf("Enter the first number: ");
    scanf("%d", &num1);
    printf("Enter the second number: ");
    scanf("%d", &num2);
    printf("Enter the third number: ");
    scanf("%d", &num3);

    // Assign the addresses of num1, num2, and num3 to the pointers
    ptr1 = &num1;
    ptr2 = &num2;
    ptr3 = &num3;

    // Find the largest number using pointers
    largest = ptr1; 

    if (*ptr2 > *largest) {
        largest = ptr2; // Update largest if num2 is greater
    }

    if (*ptr3 > *largest) {
        largest = ptr3; // Update largest if num3 is greater
    }

    // Print the largest number
    printf("The largest of %d, %d, and %d is: %d\n", *ptr1, *ptr2, *ptr3, *largest);

    return 0;
}

Explanation:

• int *ptr1, *ptr2, *ptr3: Declares three pointers to store the addresses of the three integers num1, num2, and num3.
• largest = ptr1: Assumes the first number is the largest initially.
• The program then compares the second (num2) and third (num3) numbers with the current largest and updates the largest pointer accordingly.
• *largest: Dereferences the pointer to access and print the largest number.

Sample Output:

Enter the first number: 10
Enter the second number: 25
Enter the third number: 15
The largest of 10, 25, and 15 is: 25

4. Program: Pointer Arithmetic in C

#include <stdio.h>

int main() {
    int arr[5] = {10, 20, 30, 40, 50};  
    int *ptr = arr; 

    // Accessing elements using pointer
    printf("Initial pointer points to the first element: %d\n", *ptr);
    ptr++;
    printf("After incrementing, pointer points to the second element: %d\n", *ptr);
    ptr++;
    printf("After incrementing again, pointer points to the third element: %d\n", *ptr);
    ptr--;
    printf("After decrementing, pointer points back to the second element: %d\n", *ptr);

    ptr = arr;  // Reset pointer to the first element
    printf("Accessing the last element using pointer arithmetic: %d\n", *(ptr + 4));

    // Printing all elements of the array using the pointer and pointer arithmetic
    printf("All elements of the array:\n");
    for (int i = 0; i < 5; i++) {
        printf("Element %d: %d\n", i, *(ptr + i));  
    }
    return 0;
}

Explanation:

• ptr = arr: The pointer ptr is initialized to point to the first element of the array arr.
• ptr++: Incrementing the pointer moves it to the next element in the array (increments by the size of the data type, here int).
• ptr--: Decrementing the pointer moves it back to the previous element.
• *(ptr + 4): Accesses the fifth element of the array using pointer arithmetic.
• The program also demonstrates how to iterate over the array elements using pointer arithmetic inside a loop.

Sample Output:

Initial pointer points to the first element: 10
After incrementing, pointer points to the second element: 20
After incrementing again, pointer points to the third element: 30
After decrementing, pointer points back to the second element: 20
Accessing the last element using pointer arithmetic: 50
All elements of the array:
Element 0: 10
Element 1: 20
Element 2: 30
Element 3: 40
Element 4: 50