📘 Section 9 — Pointer Practice

Practice using pointers with arrays and functions.

🎯 What You’ll Practice

Moving through an array using a pointer
Passing arrays to functions
Returning results from functions
Updating values through pointer parameters
Using pointers to find values inside arrays

🧪 Exercises

Exercise 1: Print Array in Reverse

Task: Write a program to print elements in an array on integers in reverse order using a pointer.

💡 Hint

Pointer can move backward using ptr--
Start from: arr + size - 1

🟢 Click to Show Solution

#include <stdio.h>

void printReverse(int arr[], int size)
{
    int *ptr = arr + size - 1;

    printf("Reverse: ");
    for (int i = 0; i < size; i++)
    {
        printf("%d ", *ptr);
        ptr--;
    }
    printf("\n");
}

int main()
{
    int arr[] = {1, -2, 3, 4, -5, 3, 1};
    int size = sizeof(arr) / sizeof(arr[0]);

    printReverse(arr, size);

    return 0;
}

Exercise 2: Sum of Array Elements

Task: Write a function that calculates the sum of an array using pointers.

💡 Hint

Use pointer arithmetic: *(arr + i)
Accumulate values in a sum variable

🟢 Click to Show Solution

int sumArray(int arr[], int size)
{
    int sum = 0;

    for (int i = 0; i < size; i++)
    {
        sum += *(arr + i);
    }

    return sum;
}

Exercise 3: Count Even Numbers

Task: Write a function that counts how many elements are even in an array.

💡 Hint

Even number condition: % 2 == 0
Traverse using pointer instead of indexing

🟢 Click to Show Solution

int countEven(int arr[], int size)
{
    int count = 0;

    for (int i = 0; i < size; i++)
    {
        if (*(arr + i) % 2 == 0)
        {
            count++;
        }
    }

    return count;
}

Exercise 4: Count Positive and Negative Numbers

Task: Write a function that counts positive and negative numbers in an array using pointers.

💡 Hint

Use pointers to modify values: (*pos)++
Check: > 0 and < 0

🟢 Click to Show Solution

void countPosNeg(int arr[], int size, int *pos, int *neg)
{
    *pos = 0;
    *neg = 0;

    for (int i = 0; i < size; i++)
    {
        if (*(arr + i) > 0)
            (*pos)++;
        else if (*(arr + i) < 0)
            (*neg)++;
    }
}

Exercise 5: Find Maximum and Minimum

Task: Write a function that takes an integer array and its size as parameters and updates two integer pointers to point to the maximum and minimum values in the array.

💡 Hint

Start with first element as initial max and min
Compare each element and update values using *

🟢 Click to Show Solution

void findMinMax(int arr[], int size, int *maxPtr, int *minPtr)
{
    *maxPtr = arr[0];
    *minPtr = arr[0];

    for (int i = 1; i < size; i++)
    {
        if (arr[i] > *maxPtr)
            *maxPtr = arr[i];

        if (arr[i] < *minPtr)
            *minPtr = arr[i];
    }
}

Exercise 6: Palindrome Array

Task: Write a function that checks if an array is a palindrome using pointers.

💡 Hint

Use two pointers: start & end
Move inward: start++, end--

🟢 Click to Show Solution

int isPalindrome(int arr[], int size)
{
    int *start = arr;
    int *end = arr + size - 1;

    while (start < end)
    {
        if (*start != *end)
            return 0;

        start++;
        end--;
    }

    return 1;
}

Exercise 7: Count Numbers Greater Than Average

Task: Write a function that counts how many numbers are greater than the average of the array.

💡 Hint

First compute sum → then average
Compare each element with average

🟢 Click to Show Solution

int countGreaterThanAvg(int arr[], int size)
{
    int sum = 0;

    for (int i = 0; i < size; i++)
    {
        sum += *(arr + i);
    }

    float avg = (float)sum / size;

    int count = 0;
    for (int i = 0; i < size; i++)
    {
        if (*(arr + i) > avg)
            count++;
    }

    return count;
}

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