How to multiply two matrices using pointers in C?


Pointer is a variable that stores the address of another variable.

Features of Pointers

  • Pointer saves the memory space.
  • The execution time of a pointer is faster because of the direct access to a memory location.
  • With the help of pointers, the memory is accessed efficiently i.e. memory is allocated and deallocated dynamically.
  • Pointers are used with data structures.

Pointer declaration, initialization and accessing

Consider the following statement −

int qty = 179;

In the memory, the variable can be represented as shown below −

Declaration

Declaring a pointer can be done as shown below −

Int *p;

It means ‘p’ is a pointer variable which holds the address of another integer variable.

Initialization

The address operator (&) is used to initialize a pointer variable.

For example,

int qty = 175;
int *p;
p= &qty;

Accessing a variable through its pointer

To access the value of the variable, indirection operator (*) is used.

Example

Following is the C program to multiply the two matrices by using pointers −

 Live Demo

#include <stdio.h>
#define ROW 3
#define COL 3
/* Function declarations */
void matrixInput(int mat[][COL]);
void matrixPrint(int mat[][COL]);
void matrixMultiply(int mat1[][COL], int mat2[][COL], int res[][COL]);
int main() {
   int mat1[ROW][COL];
   int mat2[ROW][COL];
   int product[ROW][COL];
   printf("Enter elements in first matrix of size %dx%d
", ROW, COL);    matrixInput(mat1);    printf("Enter elements in second matrix of size %dx%d
", ROW, COL);    matrixInput(mat2);    matrixMultiply(mat1, mat2, product);    printf("Product of both matrices is :
");    matrixPrint(product);    return 0; } void matrixInput(int mat[][COL]) {    int row, col;    for (row = 0; row < ROW; row++) {       for (col = 0; col < COL; col++) {          scanf("%d", (*(mat + row) + col));       }    } } void matrixPrint(int mat[][COL]) {    int row, col;    for (row = 0; row < ROW; row++) {       for (col = 0; col < COL; col++) {          printf("%d ", *(*(mat + row) + col));       }       printf("
");    } } void matrixMultiply(int mat1[][COL], int mat2[][COL], int res[][COL]) {    int row, col, i;    int sum;    for (row = 0; row < ROW; row++) {       for (col = 0; col < COL; col++) {          sum = 0;          for (i = 0; i < COL; i++) {             sum += (*(*(mat1 + row) + i)) * (*(*(mat2 + i) + col));          }          *(*(res + row) + col) = sum;       }    } }

Output

When the above program is executed, it produces the following output −

Enter elements in first matrix of size 3x3
2 3 1
2 5 6
2 6 8
Enter elements in second matrix of size 3x3
1 2 1
2 3 4
5 6 7
Product of both matrices is :
13 19 21
42 55 64
54 70 82

Updated on: 25-Mar-2021

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