Thread: Matrix Mulitplication

Since this is for a course you are taking, I can only assume they've been teaching what you need to know to write such a program. At the very least, reading and understanding the course text should give you what you need.

You will have a hard time getting someone to do your home work for you on these boards (but some do it anyway, unfortunately).

If you post a specific problem with how to approach a design, trouble with a piece of code or a compiler error - this forum will hop on it with a quickness.

Assuming you've compiled the code you've posted, you already know that your Matrix_x declarations won't compile. When you declare the size of an array (or matrix) in C, the expression within [] must be constant. Since you know you won't have a matrix bigger than 4x4, you can go ahead and declare your matrix's as 4x4. You know the true limits of the matrix's in R, C, and C2.

You are going to have to use loops to perform the input and the multiplication itself. I'd suggest you look up "for" loops. As for how do you enter the matrix data - I'll suggest something like this:

Code:

Enter row 1 of matrix A (3 columns): 1 2 3
Enter row 2 of matrix A (3 columns): 4 5 6
<etc...>

Where everything after the ":" is input from the user.

Use code tags next time you post code and welcome to the C Boards.

gg

Thanks for the help, sorry about the code tags, didnt realise at first but hoped it has come up in a re-edit? Anyhow i solved the input method (i think) using do while loops and can happily input values into my matrix array , however is there a way to display the array using printf in a nice square display ( coded for different size matrices). I attempted to do this using a for loop but it would only print one line of elements that are the diagonal elements from top left to right. Heres what ive done so far

Code:

include <stdio.h>
#define MAX_R 4
#define MAX_C 4
#define MAX_C2 4

int main()
{
	int R = 0, C = 0, C2 = 0;
	int r_i = 0, c_i = 0, c2_i = 0;
	int Matrix_A [MAX_R] [MAX_C];
	int x = 0, y = 0;
	printf("This program will multiply 2 matrices (up to the order or 4x4),and display the result\n");
	do {
	printf("Enter the number of rows in matrix A\n");

	scanf ("%d", &R);
	if (R>4)
	{
	printf("Number or rows too great\n");
	}

	} while (R>4);
	do {
	 printf("Enter the number of colums in matrix A\n");

	 scanf ("%d", &C);
	 if (C>4)
	 {
	 printf("number of colums too great\n");
	 }

	 } while (C>4);
	 do {
	 printf("Enter the number of colums in Matrix B\n");

	 scanf ("%d", &C2);
	 if (C2>4)
	 {
	 printf("number of colums too great\n");
	 }
	 } while (C2>4);

	do  {
	printf("\nFor row %d of Matrix A",r_i +1);
	while(c_i < (C)) {
		printf("\n\tEnter the value for column %d :",c_i +1);

		scanf("%d",&Matrix_A [r_i] [c_i]);
		++c_i;
		}
		c_i = 0;
		++r_i;
	}while (r_i < R);



	for(x=0, y=0; x<R, y<C; ++x, ++y)
	{

		printf("%3d",Matrix_A [x] [y]);
		if ( x != 1 && x !=2 && x !=3 && x !=4 )
		continue;
		printf("\n");


	}


	return (0);


}

In response to it being for a course, yes i know i have the material avalible to learn this from, its just its not presented in a reader friendly manner and actually having somone point me towards the right area helps a great deal.
So any pointers would be apprciated ,
thanks in advance

P.S congrats on a great board, good design and obvvious hogh participation

Ok the for loop out and it now displays all the elements but still cant get them in a nice matrix square, tried newling to get the effect but not with sucess, also now matrix A disply runs into the start of entering matrix B, can some1 suggest when i need to tell the printf to newline? thanks for all the help so far, its been brilliant, im learning more C here then i did in 10 weeks of course lectures !
so far:

Code:

#include <stdio.h>
#define MAX_R 4
#define MAX_C 4
#define MAX_C2 4
#define MAX_R2 4
int main()
{
	int R = 0, C = 0, R2 = 0, C2 = 0;
	int r_i = 0, c_i = 0, c2_i = 0, r2_i = 0;
	int Matrix_A [MAX_R] [MAX_C];
	int Matrix_B [MAX_R2] [MAX_C2];
	int Matrix_C [MAX_R] [MAX_C2];
	int x = 0, y = 0;
	printf("This program will multiply 2 matrices (up to the order or 4x4),and display the result\n");
	do {
	printf("Enter the order of Matrix A in the format NxN:\n");

	scanf ("%dx%d",&R ,&C);
	if (R>4 || C>4)
	{
	printf("Order too great\n");
	}

	} while (R>4 || C>4);

	do  {
	printf("\nFor row %d of Matrix A",r_i +1);
	while(c_i < C) {
		printf("\n\tEnter the value for column %d :",c_i +1);

		scanf("%d",&Matrix_A [r_i] [c_i]);
		++c_i;
		}
		c_i = 0;
		++r_i;
	}while (r_i < R);



	for(x=0; x<R; x++){
	for(y=0; y<C; y++)
	{

		printf("\t\n%3d",Matrix_A [x] [y]);
		if ( (x == 0 && y == 0) ||  (x ==1 && y == 0))

		printf("\n");


	}
	do {
	printf("Enter the order of Matrix B in the format NxN:\n");
	scanf ("%dx%d",&R2 ,&C2);
	if (R2>4 || C2>4)
	{
	printf("Order tpp great\n");
	}
	}while (R2>4 || C2>4);
	do {
	printf("\nFor row %d of Matrix B",r2_i +1);
	while(c2_i < C2) {
		printf("\n\tEnter the value for column %d :",c2_i +1);

		scanf("%d",&Matrix_B [r2_i] [c2_i]);
		++c2_i;
		}
		c2_i = 0;
		++r2_i;
	}while (r2_i < R2);

	for(x=0; x<R2; x++){
	for(y=0; y<C2; y++)
	{
		printf("%3d",Matrix_B [x] [y]);

	}
	}

	return (0);



}
}