🟡 Intermediate · Lesson 25

Pointers & Arrays

Pointers और Arrays

Pointer and Array Relationship

In C, arrays and pointers are closely related. The array name usually represents the address of the first element. Because of this, array elements can be accessed using both index notation and pointer notation.

💡 Key Idea

arr[i] is internally similar to *(arr + i). Both access the same element.

Array Name as Pointer

C Language

#include <stdio.h>

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

    printf("Address of first element = %p\n", (void*)&arr[0]);
    printf("Array name address       = %p\n", (void*)arr);
    printf("First element            = %d\n", *arr);
    printf("Third element            = %d\n", *(arr + 2));

    return 0;
}

Address of first element = 0x... Array name address = 0x... First element = 10 Third element = 30

⚠️ Important Difference

arr behaves like a pointer in expressions, but it is not a modifiable pointer variable. You cannot write arr++, but you can write ptr++.

Pointer Arithmetic with Arrays

When an integer pointer is increased by 1, it moves to the next integer element, not the next byte. The compiler automatically uses the size of the data type.

C Language

#include <stdio.h>

int main() {
    int marks[] = {85, 90, 78, 92};
    int *p = marks;

    for(int i = 0; i < 4; i++) {
        printf("marks[%d] = %d\n", i, *(p + i));
    }

    return 0;
}

marks[0] = 85 marks[1] = 90 marks[2] = 78 marks[3] = 92

Passing Arrays to Functions

When an array is passed to a function, actually the address of its first element is passed. Therefore, changes made inside the function can affect the original array.

C Language

#include <stdio.h>

void update(int *a, int n) {
    for(int i = 0; i < n; i++) {
        a[i] = a[i] + 5;
    }
}

void display(int a[], int n) {
    for(int i = 0; i < n; i++) {
        printf("%d ", *(a + i));
    }
}

int main() {
    int arr[] = {10, 20, 30};
    update(arr, 3);
    display(arr, 3);
    return 0;
}

15 25 35

Summary

arr normally gives the base address of the array
arr[i] and *(arr+i) access the same value
Pointer arithmetic moves according to data type size
Arrays passed to functions can be handled using pointers
Array name is not a modifiable pointer, so arr++ is invalid

🏋️ Practice

Write programs to find sum, maximum, minimum and reverse of an array using pointers.

Pointer और Array Relationship

C में arrays और pointers का बहुत close relation होता है। Array का नाम अक्सर first element का address represent करता है। इसलिए array elements को index और pointer दोनों methods से access कर सकते हैं।

💡 मुख्य बात

arr[i] लगभग *(arr + i) जैसा ही काम करता है। दोनों same element access करते हैं।

Array Name as Pointer

C Language

#include <stdio.h>

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

    printf("First element address = %p\n", (void*)&arr[0]);
    printf("Array name address    = %p\n", (void*)arr);
    printf("First value           = %d\n", *arr);
    printf("Third value           = %d\n", *(arr + 2));

    return 0;
}

⚠️ ध्यान दें

arr expression में pointer की तरह behave करता है, पर यह modifiable pointer variable नहीं है। इसलिए arr++ invalid है।

Pointer Arithmetic

Pointer में 1 add करने पर वह next element पर जाता है। जैसे int * pointer next integer पर जाएगा।

C Language

#include <stdio.h>

int main() {
    int marks[] = {85, 90, 78, 92};
    int *p = marks;

    for(int i = 0; i < 4; i++) {
        printf("%d ", *(p + i));
    }
    return 0;
}

85 90 78 92

Array को Function में भेजना

Function में array भेजने पर उसका base address जाता है। इसलिए function के अंदर changes original array को affect कर सकते हैं।

C Language

void change(int *a, int n) {
    for(int i = 0; i < n; i++)
        a[i] += 10;
}

सारांश

Array name base address देता है
arr[i] और *(arr+i) same value access करते हैं
Pointer arithmetic data type size के अनुसार move करती है
Array function में pointer की तरह pass होता है
Practice के लिए sum, max, reverse pointer से करें

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