C language - usage of struct to form Matrix - c

Question

I know that object oriented is not welcoming in c language but I still trying to work my way because it is possible as later languages based on c works good with objects
so my question is when I try to write a function outside of main it doesnt give me access and doesnt change values of wanted structs , see code below (I marked every things and included working functions inside the main) :
#include <stdio.h>
#include <stdlib.h>
static int RandomNum() {
int generate = rand() / 100000000;
while (generate >= 9) {
generate = rand() / 100000000;
}
return generate;
}
// Object Definition
typedef struct {
int a, b;
int Mat[2][4];
} Matrix2x4;
typedef struct {
int a, b;
int Mat[4][5];
} Matrix4x5;
typedef struct {
int a, b;
int Mat[4][5];
} Matrix2x5;
void PrintMat2x4(Matrix2x4 a) {
int row = a.a;
int col = a.b;
for (int i = 0; i < row; i++) {
printf("{%s", " ");
for (int j = 0; j < col; j++) {
printf("%d ,", a.Mat[i][j]);
}
printf("}%s\n", " ");
}
}
void PrintMat4x5(Matrix4x5 a) {
int row = a.a;
int col = a.b;
for (int i = 0; i < row; i++) {
printf("{%s", " ");
for (int j = 0; j < col; j++) {
printf("%d ,", a.Mat[i][j]);
}
printf("}%s\n", " ");
}
}
void PrintMat2x5(Matrix2x5 a) {
int row = a.a;
int col = a.b;
for (int i = 0; i < row; i++) {
printf("{%s", " ");
for (int j = 0; j < col; j++) {
printf("%d ,", a.Mat[i][j]);
}
printf("}%s\n", " ");
}
}
// NOT WORKING AS A SEPERATE FUNCTION SO I PUT IT INSIDE THE MAIN
/*static void MatrixMultiplication (Matrix2x4 a , Matrix4x5 b , Matrix2x5 c) {
for (int i = 0; i < a.b; i++){
for (int j = 0; j < b.b; j++){
for (int k = 0; k < a.b; k++){
c.Mat[i][j] = c.Mat[i][j]+(a.Mat[i][k]*b.Mat[k][j]);}}}
}
void setRandom (Matrix a) {
int row = ((int)(sizeof (a.Mat) / sizeof (a.Mat)[0])) ;
int col = ((int)(sizeof (a.Mat)[0] / sizeof (a.Mat)[0][0])) ;
for (int i = 0; i < row ; i++){
for (int j = 0; j < col; j++){
a.Mat[i][j] = RandomNum();}}}*/
void main() {
printf("%s\n\n", "Start..");
Matrix2x4 test = {2,4,{0}}; // <----- SIZE IS 2X4
int row = ((int)(sizeof(test.Mat) / sizeof(test.Mat)[0]));
int col = ((int)(sizeof(test.Mat)[0] / sizeof(test.Mat)[0][0]));
for (int i = 0; i < row; i++) {
for (int j = 0; j < col; j++) {
test.Mat[i][j] = RandomNum();
}
}
Matrix4x5 test2 = {4,5,{0}}; // <----- SIZE IS 4X5
int row2 = ((int)(sizeof(test2.Mat) / sizeof(test2.Mat)[0]));
int col2 = ((int)(sizeof(test2.Mat)[0] / sizeof(test2.Mat)[0][0]));
for (int i = 0; i < row2; i++) {
for (int j = 0; j < col2; j++) {
test2.Mat[i][j] = RandomNum();
}
}
Matrix2x5 mult = {2,5,{0}}; // <----- SIZE IS 2X5
PrintMat2x4(test);
printf("X\n");
PrintMat4x5(test2);
printf("=\n");
for (int i = 0; i < test.b; i++) {
for (int j = 0; j < test2.b; j++) {
for (int k = 0; k < test.b; k++) {
mult.Mat[i][j] = mult.Mat[i][j] + (test.Mat[i][k] * test2.Mat[k][j]);
}
}
}
PrintMat2x5(mult);
printf("\n\n%s", "End ---> ");
}

Answer 1

In order for this function to work:
static void MatrixMultiplication (Matrix2x4 a , Matrix4x5 b , Matrix2x5 c) {
for (int i = 0; i < a.b; i++){
for (int j = 0; j < b.b; j++){
for (int k = 0; k < a.b; k++){
c.Mat[i][j] = c.Mat[i][j]+(a.Mat[i][k]*b.Mat[k][j]);}}}
}
You must pass your structs as pointers:
static void MatrixMultiplication (Matrix2x4* a , Matrix4x5* b , Matrix2x5* c) {
for (int i = 0; i < a->b; i++){
for (int j = 0; j < b->b; j++){
for (int k = 0; k < a->b; k++){
c->Mat[i][j] = c->Mat[i][j]+(a->Mat[i][k]*b->Mat[k][j]);}}}
}
Your original function doesn't work outside of main, because C is making a copy of those structs for the function's own use. Therefore the original structs never get modified. Changing those parameters to pointers means that the function is working with the original structs.