C program of Matrix Multiplication using Pointers : Let us discuss how to multiply M x N matrix using a C program. First of all we need to understand how an M x N matrix multiplication takes place. Matrix multiplication is a binary operation that takes a pair of matrices, and produces another matrix as output. Matrix is basically a two dimensional array. Let us see by an example how to multiply a matrix by another matrix :

As above shown, matrix multiplication consists a concept of dot products of rows and columns.

So this is the resultant matrix obtained after multiplication :

Now lets see how we are going to implement above logic of multiplying matrices in C using pointers.

C program of Matrix Multiplication using Pointers :

#include <stdio.h> 
#include <stdlib.h> 

//Define functions that will be used in the program 
void multiplyMatrices(); 
void getRowColumn(int *row, int *col, char *matrix); 
int *createMatrix(int *row, int *col); 
void getMatrixValues(int *source, int row, int col, char *name); 
int *destroyMatrix(int *matrix); 
void printMatrix(const int *source, int row, int col); 

//Start of main 
int main() 
{ 
//Call multiplyMatrices function 
multiplyMatrices(); 
//End main 
return(0); 
//End of main 
} 

//Start of multiplyMatrices function 
void multiplyMatrices() 
{ 
//Declare variables 
int oneRow, oneCol, twoRow, twoCol, i, j, k; 

//Call getRowColumn to ask user for the matrix size for both matrices 
getRowColumn(&oneRow, &oneCol, "Matrix 1"); 
getRowColumn(&twoRow, &twoCol, "Matrix 2"); 

//The number of columns in oneMatrix must equal the number of rows in twoMatrix 
if(oneCol != twoRow) 
{ 
printf("The number of columns in the first matrix must equal the number of rows in the second matrix.\n"); 
exit(EXIT_FAILURE); 
} 

//Create the arrays in the heap memory 
int *oneMatrix = createMatrix(&oneRow, &oneCol); 
int *twoMatrix = createMatrix(&twoRow, &twoCol); 
int *multipliedMatrix = createMatrix(&oneRow, &twoCol); 

//Declare pointer variables to store the initial locations of 
//my arrays for later use 
int *initialOneMatrix, *initialTwoMatrix, *initialMultipliedMatrix; 
initialOneMatrix = oneMatrix; 
initialTwoMatrix = twoMatrix; 
initialMultipliedMatrix = multipliedMatrix; 

//Ask user for the values of each matrix 
getMatrixValues(oneMatrix, oneRow, oneCol, "Matrix 1"); 
getMatrixValues(twoMatrix, twoRow, twoCol, "Matrix 2"); 

//Multiply the matrices (took me like 5 hours in 
//the debugger to figure out how to arrange these loops lol) 
//A for loop while i is less than oneRow(number of rows in first matrix) 
for(i = 0; i < oneRow; i++) 
{ 
//A for loop while j is less than twoCol 
for(j = 0; j < twoCol; j++) 
{ 
//Increment the address of oneMatrix by its number of columns multiplied by i 
oneMatrix += (oneCol * i); 
//Increment the address of twoMatrix by j 
twoMatrix += j; 

//A for loop while k is less than oneCol 
for(k = 0; k < oneCol; k++) 
{ 
//Multiply the current entries of the matracies and add the answer to the current entry for the multiplied matrix 
*multipliedMatrix += *oneMatrix * *twoMatrix; 
//Increment oneMatrix by 1 
oneMatrix++; 
//Increment twoMatrix by the number of its columns 
twoMatrix += twoCol; 
} 
//Increment multipliedMatrix 
multipliedMatrix++; 
//"Rewind" oneMatrix to its original address 
oneMatrix = initialOneMatrix; 
//"Rewind" twoMatrix to its original address 
twoMatrix = initialTwoMatrix; 
} 
} 

//"Rewind" multipliedMatrix to its original address 
multipliedMatrix = initialMultipliedMatrix; 

//Newline to make it pretty 
printf("\n"); 
//Call printMatrix function to print oneMatrix 
printMatrix(oneMatrix, oneRow, oneCol); 
//Newline, multiplication symbol, and two more newlines to make it pretty 
printf("\n*\n\n"); 
//Call printMatrix function to print twoMatrix 
printMatrix(twoMatrix, twoRow, twoCol); 
//Newline, equal sign, and two more newlines to make it pretty 
printf("\n=\n\n"); 
//Call printMatrix function to print multipliedMatrix 
printMatrix(multipliedMatrix, oneRow, twoCol); 

//Call destroyMatrix function to clear clear all of the matrices from memory 
destroyMatrix(oneMatrix); 
destroyMatrix(twoMatrix); 
destroyMatrix(multipliedMatrix); 

return; 
//End of multiplyMatrices 
} 

//Start of getRowColumn function 
void getRowColumn(int *row, int *col, char *matrix) 
{ 
//Ask user how many rows for the specified matrix 
printf("Please enter the number of rows for %s\n", matrix); 
//Set variable 'row' to what the user input 
scanf("%d", row); 
//Ask user how many columns for the specified array 
printf("Please enter the number of columns for %s\n", matrix); 
//Set variable 'col' to what the user input 
scanf("%d", col); 
//End of getRowColumn 
} 

//Start of createMatrix function 
int *createMatrix(int *row, int *col) 
{ 
//Initialize the new matrix in the heap memory using calloc with row times 
//col for an argument and using sizeof to let calloc know the size of int 
int *newMatrix = calloc(*row * *col, sizeof(int)); 

//Check if newMatrix is nonexistent, if so the memory 
//was unable to allocate and exit the program 
if(!newMatrix) 
{ 
printf("Unable to allocate memory.\n"); 
exit(EXIT_FAILURE); 
} 

//Return the newMatrix to where the function was called 
return(newMatrix); 
//End of createMatrix 
} 

//Start of getMatrixValues 
void getMatrixValues(int *source, int row, int col, char *name) 
{ 
//Declare counting variables for the for loops 
int i, j; 

//For loop to cycle through the rows 
for(i = 0; i < row; i++) 
{ 
//For loop to cycle through the columns 
for(j = 0; j < col; j++) 
{ 
//Ask user for a value for the specified entry 
printf("Enter the value for %d %d for %s\n", i, j, name); 
//Set source to what the user input, then increment source by 1 
scanf("%d", source++); 
} 
} 
//End of getMatrixValues 
} 

//Start of destroyMatrix function 
int *destroyMatrix(int *matrix) 
{ 
//Check if matrix exists 
if(matrix) 
{ 
//Function to free the matrix from memory 
free(matrix); 
} 
return(NULL); 
//End of destroyMatrix 
} 

//Start of printMatrix function 
void printMatrix(const int *source, int row, int col) 
{ 
//Declare counting variables for the for loops 
int i, j; 

//Cycle through the rows 
for(i = 0; i < row; i++) 
{ 
//Print beginning "side" to the matrix 
printf("|"); 
//Cycle through the columns 
for(j = 0; j < col; j++) 
{ 
//Print the specified matrix entry 
printf("%5d", *source++); 
} 
//Print an ending "side" to the matrix with a newline 
printf("|\n"); 
} 
//End of printMatrix 
}

 I hope you all have enjoyed the code. Special thanks to Apoc and Miss Pelling for code. If you have any queries or doubts ask us in form of comments.