Matrix Multiplication function won't compile inside the main - c

Question

This is a simple matrix multiplication, code won't compile. I also want to take the function outside. I know I have to have global variables and function declaration, but the code won't even compile inside the main.
#include<stdio.h>
#include<stdlib.h>
#include<math.h>
#define N 10
float *A[N], *B[N], *C[N];
int main(){
int count = 0, i,j, k;
for (i = 0; i < N; i++)
A[i] = (float*)malloc(N * sizeof(float));
for (i = 0; i < N; i++)
B[i] = (float*)malloc(N * sizeof(float));
for (i = 0; i < N; i++)
C[i] = (float*)malloc(N * sizeof(float));
for (i = 0; i < N; i++)
for (j = 0; j < N; j++){
A[i][j] = ++count;
B[i][j] = count;
}
void multiply(float* A, float* B, int n) {
for(int i=0; i<n; i++)
for(int j=0; j<n; j++)
for(int k=0; k<n; k++)
C[i][j] += A[i][k] * B[k][j];
}
for (i = 0; i < N; i++)
for (j = 0; j < N; j++)
printf("%f\t", C[i][j] );
}

Answer 1

Your multiply function definition inside main makes it a nested function which is not allowed in C. You can call as many functions inside a function but cannot define a new function inside an already existing one.
Plus you have also not called the multiply function.

Answer 2

A , B and C are defined at the top as global as an array of pointers to float
inside your multiply function you have locally redefined them as a pointer to a float..
this is why the multiplication fails inside multiply.
you are pretending that A and B are arrays of pointers to float again.. and they have been locally scoped as pointers to float.
Does this do what you were expecting ?
#include<stdio.h>
#include<stdlib.h>
#include<math.h>
#define N 10
float *A[N], *B[N], *C[N];
void multiply( float *a[], float *b[], float *c[], int n )
{
for(int i=0; i<n; i++)
for(int j=0; j<n; j++)
for(int k=0; k<n; k++)
c[i][j] += (a[i][k]) * b[k][j];
}
int main(){
int count = 0, i,j, k;
for (i = 0; i < N; i++)
A[i] = (float*)malloc(N * sizeof(float));
for (i = 0; i < N; i++)
B[i] = (float*)malloc(N * sizeof(float));
for (i = 0; i < N; i++)
C[i] = (float*)malloc(N * sizeof(float));
for (i = 0; i < N; i++)
for (j = 0; j < N; j++)
{
A[i][j] = ++count;
B[i][j] = count;
}
multiply(A,B, C, N);
for (i = 0; i < N; i++)
for (j = 0; j < N; j++)
printf("%f\t", C[i][j] );
}
if so please explain it back to me how this works