Input matrix in C using function - c

Question

I am trying to input a matrix of order p*q using a function I got some errors. how to get the input using a pointer it gives me a segmentation fault .
#include<stdio.h>
int read_matrix(int *x,int p,int q){
for(int i=0;i<p;i++){
for(int j=0;j<q;j++){
scanf("%d",*(x+i)+j);
}
}
return 0;
}
int main(){
int p,q;
printf("enter the order of the matrix");
scanf("%d%d",&p,&q);
int a[p][q];
read_matrix(a[q],p,q);
for(int i=0;i<p;i++){
for(int j=0;j<q;j++)
printf("%d",a[i][j]);
}
}

Answer 1

You have multiple problems and seem to misunderstand how arrays and pointers work. To begin with a[q] will be out of bounds if p <= q.
a[q] (if q is valid) is an array of q elements, which decays to a pointer to its first element. It's not any kind of pointer to the matrix itself.
And inside the read_matrix function when you do *(x + i) + j that is actually equal to x[i] + j which is a single int value, and not a pointer to an element in any array.
You need to pass the matrix itself to the function, and let it decay to a pointer to an array, and use that as a proper "array of arrays":
// Use variable-length arrays for the matrix argument x
// Declare it as a pointer to an array of q integer elements
// Note the changed order of arguments, it's needed because q must be declared
// before its used for the VLA
void read_matrix(int p, int q, int (*x)[q]) {
for (int i = 0; i < p; ++i) {
for (int j = 0; j < q; ++j) {
scanf("%d", &x[i][j]); // Use normal array indexing and address-of operator
}
}
}
int main(void) {
int p, q;
scanf("%d %d", &p, &q);
int a[p][q];
// Here a will decay to a pointer to its first element, &a[0]
// Since a[0] is an array of q elements, the type will be
// int (*)[q], exactly as expected by the function
read_matrix(p, q, a);
for (int i = 0; i < p; ++i) {
for (int j = 0; j < q; ++j) {
printf("%d ", x[i][j]);
}
printf("\n");
}
}

Answer 2

You are making things needlessly complicated with the pointer arithmetic. *(x+i)+j means x[i] + j*sizeof(int) which is not what you want.
Just do something like this instead:
#include<stdio.h>
void read_matrix(int x, int y, int matrix[x][y])
{
int count=0;
for(int i=0;i<x;i++)
for(int j=0;j<y;j++)
matrix[i][j] = ++count;
}
int main (void)
{
int x=3, y=2;
int matrix[x][y];
read_matrix(x,y,matrix);
for(int i=0;i<x;i++)
{
for(int j=0;j<y;j++)
printf("%d ",matrix[i][j]);
printf("\n");
}
}