Home - News ( United States | United Kingdom | Italy | Germany ) - Football scores

Showing content from https://www.geeksforgeeks.org/c/pointer-arithmetics-in-c-with-examples/ below:

Pointer Arithmetics in C with Examples

Pointer Arithmetic is the set of valid arithmetic operations that can be performed on pointers. The pointer variables store the memory address of another variable. It doesn't store any value. 

Hence, there are only a few operations that are allowed to perform on Pointers in C language. The C pointer arithmetic operations are slightly different from the ones that we generally use for mathematical calculations. These operations are:

1. Increment/Decrement of a Pointer
2. Addition of integer to a pointer
3. Subtraction of integer to a pointer
4. Subtracting two pointers of the same type
5. Comparison of pointers

Increment: It is a condition that also comes under addition. When a pointer is incremented, it actually increments by the number equal to the size of the data type for which it is a pointer. 

For Example:
If an integer pointer that stores address 1000 is incremented, then it will increment by 4(size of an int), and the new address will point to 1004. While if a float type pointer is incremented then it will increment by 4(size of a float) and the new address will be 1004.

Decrement: It is a condition that also comes under subtraction. When a pointer is decremented, it actually decrements by the number equal to the size of the data type for which it is a pointer. 

For Example:
If an integer pointer that stores address 1000 is decremented, then it will decrement by 4(size of an int), and the new address will point to 996. While if a float type pointer is decremented then it will decrement by 4(size of a float) and the new address will be 996.

Note: It is assumed here that the architecture is 64-bit and all the data types are sized accordingly. For example, integer is of 4 bytes.

Below is the program to illustrate pointer increment/decrement:

#include <stdio.h>
// pointer increment and decrement
// pointers are incremented and decremented 
// by the size of the data type they point to 
int main(){
    int a = 22;
    int *p = &a;
    
    // p = 6422288
    printf("p = %u\n", p); 
    p++;
    // p++ = 6422292    +4 
    // 4 bytes
    printf("p++ = %u\n", p); 
    p--;
    
    // p-- = 6422288     -4    
    // restored to original value
    printf("p-- = %u\n", p); 
    float b = 22.22;
    float *q = &b;
    
    // q = 6422284
    printf("q = %u\n", q);  
    q++;
    
    // q++ = 6422288      +4   
    // 4 bytes
    printf("q++ = %u\n", q); 
    q--;
    
    // q-- = 6422284       -4  
    // restored to original value
    printf("q-- = %u\n", q); 

    char c = 'a';
    char *r = &c;
    
    // r = 6422283
    printf("r = %u\n", r);   
    r++;
    
    // r++ = 6422284     +1   
    // 1 byte
    printf("r++ = %u\n", r);   
    r--;
    
    //r-- = 6422283     -1  
    // restored to original value
    printf("r-- = %u\n", r);   

    return 0;
}

p = 1441900792
p++ = 1441900796
p-- = 1441900792
q = 1441900796
q++ = 1441900800
q-- = 1441900796
r = 1441900791
r++ = 1441900792
r-- = 1441900791

Note: Pointers can be outputted using %p, since, most of the computers store the address value in hexadecimal form using %p gives the value in that form. But for simplicity and understanding we can also use %u to get the value in Unsigned int form.

When a pointer is added with an integer value, the value is first multiplied by the size of the data type and then added to the pointer.

For Example:
Consider the same example as above where the ptr is an integer pointer that stores 1000 as an address. If we add integer 5 to it using the expression, ptr = ptr + 5, then, the final address stored in the ptr will be ptr = 1000 + sizeof(int) * 5 = 1020.

#include <stdio.h>

int main(){
    // Integer variable
    int N = 4;

    // Pointer to an integer
    int *ptr1, *ptr2;

    // Pointer stores the address of N
    ptr1 = &N;
    ptr2 = &N;

    printf("Pointer ptr2 before Addition: ");
    printf("%p \n", ptr2);

    // Addition of 3 to ptr2
    ptr2 = ptr2 + 3;
    printf("Pointer ptr2 after Addition: ");
    printf("%p \n", ptr2);

    return 0;
}

Pointer ptr2 before Addition: 0x7ffca373da9c 
Pointer ptr2 after Addition: 0x7ffca373daa8 

When a pointer is subtracted with an integer value, the value is first multiplied by the size of the data type and then subtracted from the pointer similar to addition.

For Example:
Consider the same example as above where the ptr is an integer pointer that stores 1000 as an address. If we subtract integer 5 from it using the expression, ptr = ptr - 5, then, the final address stored in the ptr will be ptr = 1000 - sizeof(int) * 5 = 980.

Below is the program to illustrate pointer Subtraction:

#include <stdio.h>

int main(){
    // Integer variable
    int N = 4;

    // Pointer to an integer
    int *ptr1, *ptr2;

    // Pointer stores the address of N
    ptr1 = &N;
    ptr2 = &N;

    printf("Pointer ptr2 before Subtraction: ");
    printf("%p \n", ptr2);

    // Subtraction of 3 to ptr2
    ptr2 = ptr2 - 3;
    printf("Pointer ptr2 after Subtraction: ");
    printf("%p \n", ptr2);

    return 0;
}

Pointer ptr2 before Subtraction: 0x7ffd718ffebc 
Pointer ptr2 after Subtraction: 0x7ffd718ffeb0 

The subtraction of two pointers is possible only when they have the same data type. The result is generated by calculating the difference between the addresses of the two pointers and calculating how many bytes of data it is according to the pointer data type. The subtraction of two pointers gives the increments between the two pointers. 

For Example: 
Two integer pointers say ptr1(address:1000) and ptr2(address:1004) are subtracted. The difference between addresses is 4 bytes. Since the size of int is 4 bytes, therefore the increment between ptr1 and ptr2 is given by (4/4) = 1.

Below is the implementation to illustrate the Subtraction of Two Pointers:

#include <stdio.h>

int main(){
    int x = 6; 
    int N = 4;

    // Pointer declaration
    int *ptr1, *ptr2;
    
    // stores address of N
    ptr1 = &N; 
    
    // stores address of x
    ptr2 = &x; 

    printf(" ptr1 = %u, ptr2 = %u\n", ptr1, ptr2);
    // %p gives an hexa-decimal value,
    // We convert it into an 
    // unsigned int value by using %u

    // Subtraction of ptr2 and ptr1
    x = ptr1 - ptr2;

    // Print x to get the Increment
    // between ptr1 and ptr2
    printf("Subtraction of ptr1 "
           "& ptr2 is %d\n",
           x);

    return 0;
}

 ptr1 = 2715594428, ptr2 = 2715594424
Subtraction of ptr1 & ptr2 is 1

We can compare the two pointers by using the comparison operators in C. We can implement this by using all operators in C >, >=, <, <=, ==, !=.  It returns true for the valid condition and returns false for the unsatisfied condition. 

1. Step 1: Initialize the integer values and point these integer values to the pointer.
2. Step 2: Now, check the condition by using comparison or relational operators on pointer variables.
3. Step 3: Display the output.

#include <stdio.h>

int main(){
    // declaring array
    int arr[5];

    // declaring pointer to array name
    int* ptr1 = &arr;
    // declaring pointer to first element
    int* ptr2 = &arr[0];

    if (ptr1 == ptr2) {
        printf("Pointer to Array Name and First Element "
               "are Equal.");
    }
    else {
        printf("Pointer to Array Name and First Element "
               "are not Equal.");
    }

    return 0;
}

Pointer to Array Name and First Element are Equal.

A pointer can be compared or assigned a NULL value irrespective of what is the pointer type. Such pointers are called NULL pointers and are used in various pointer-related error-handling methods.

#include <stdio.h>

int main(){

    int* ptr = NULL;

    if (ptr == NULL) {
        printf("The pointer is NULL");
    }
    else {
        printf("The pointer is not NULL");
    }
    return 0;
}

The pointer is NULL

In the below approach, it results in the count of odd numbers and even numbers in an array. We are going to implement this by using a pointer.

1. Step 1: First, declare the length of an array and array elements.
2. Step 2: Declare the pointer variable and point it to the first element of an array.
3. Step 3: Initialize the count_even and count_odd. Iterate the for loop and check the conditions for the number of odd elements and even elements in an array
4. Step 4: Increment the pointer location ptr++ to the next element in an array for further iteration.
5. Step 5: Print the result.

#include <stdio.h>

int main(){
    int n = 10; 

    int arr[] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
    
    // Declaration of pointer variable
    int* ptr; 

    // Pointer points the first (0th index)
    // element in an array
    ptr = arr; 
    int count_even = 0;
    int count_odd = 0;

    for (int i = 0; i < n; i++) {

        if (*ptr % 2 == 0) {
            count_even++;
        }
        if (*ptr % 2 != 0) {
            count_odd++;
        }
        
        // Pointing to the next 
        // element in an array
        ptr++; 
    }
    printf("No of even elements in an array is : %d",
           count_even);
    printf("\nNo of odd elements in an array is : %d",
           count_odd);
}

No of even elements in an array is : 5
No of odd elements in an array is : 5

Pointers contain addresses. Adding two addresses makes no sense because there is no idea what it would point to. Subtracting two addresses lets you compute the offset between the two addresses. An array name acts like a pointer constant. The value of this pointer constant is the address of the first element.

For Example: if an array is named arr then arr and &arr[0] can be used to reference the array as a pointer.

Below is the program to illustrate the Pointer Arithmetic on arrays:

Program 1: 

#include <stdio.h>

int main(){

    int N = 5;

    // An array
    int arr[] = { 1, 2, 3, 4, 5 };

    // Declare pointer variable
    int* ptr;

    // Point the pointer to first
    // element in array arr[]
    ptr = arr;

    // Traverse array using ptr
    for (int i = 0; i < N; i++) {

        // Print element at which
        // ptr points
        printf("%d ", ptr[0]);
        ptr++;
    }
}

Program 2: 

#include <stdio.h>

// Function to traverse 2D array
// using pointers
void traverseArr(int* arr, int N, int M){

    int i, j;

    // Traverse rows of 2D matrix
    for (i = 0; i < N; i++) {

        // Traverse columns of 2D matrix
        for (j = 0; j < M; j++) {

            // Print the element
            printf("%d ", *((arr + i * M) + j));
        }
        printf("\n");
    }
}

int main(){

    int N = 3, M = 2;

    // A 2D array
    int arr[][2] = { { 1, 2 }, { 3, 4 }, { 5, 6 } };

    // Function Call
    traverseArr((int*)arr, N, M);
    return 0;
}

RetroSearch is an open source project built by @garambo | Open a GitHub Issue

Search and Browse the WWW like it's 1997 | Search results from DuckDuckGo

HTML: 3.2 | Encoding: UTF-8 | Version: 0.7.4