passing values from child to parent process using a shared file - c

Question

the following c program takes inputs for a 2D - array, and then takes a value n and multiplies every element by n. the child process iterates through the matrix, opens the file named sharedfile and then writes the value into the file. the parent process then open sharedfile and reads the values and prints them. I know there are probably better ways to accomplish this but this is the method we are learning currently.
#include <stdio.h>
#include <stdlib.h>
#include <sys/wait.h>
#include <unistd.h>
#include <fcntl.h>
int main(int argc, char *argv[]){
int row = 0;
int column = 0;
if(argc > 2){
row = atoi(argv[1]);
column = atoi(argv[2]);
}
int *A = (int *) malloc((row * column) * sizeof(int));
int i, j;
printf("Enter the matrix elements:\n");
for (i = 0; i < row; i++) {
for (j = 0; j < column; j++) {
printf("A[%d,%d] = ", i, j);
scanf("%d", A + i * column + j); //matrix elements is stored in row-wise
}
printf("\n");
}
enter n
int n = 0;
printf("Enter a number:");
scanf("%d", &n);
child process code:
char sharedfile[] = "child_result.txt";
for(int i = 0; i < row; ++i){
pid_t pid = fork();
if (pid == -1){//not able to create child
printf("parent PID %d => \n", getpid());
int Y[1000];
for (j = 0; j < column; j++) {
Y[j] = n * (*(A + i * column + j));
int fd = open(sharedfile, O_WRONLY | O_CREAT, S_IRUSR | S_IWUSR);
int byte_write = write(fd,Y,sizeof(Y));
printf("%d * A[%d,%d] = %d\n", n, i, j,byte_write);
close(fd);
exit(0);
}
}
else if (pid == 0) {//child
printf("child%d PID: %d \n", i, getpid());
int Y[1000];
for (j = 0; j < column; j++) {
Y[j] = n * (*(A + i * column + j));
int fd = open(sharedfile, O_WRONLY | O_CREAT, S_IRUSR | S_IWUSR);
int byte_write = write(fd,Y,sizeof(Y));
printf("%d * A[%d,%d] = %d\n", n, i, j,byte_write);
close(fd);
exit(0);
}
}
parent process code:
int child_exit;
wait(&child_exit);
printf("Final matrix elements:\n");
for (i = 0; i < row; i++) {
for (j = 0; j < column; j++) {
int fd = open(sharedfile,O_RDONLY);
int Y[1000];
int byte_read = read(fd,Y,sizeof(Y));
printf("A[%d,%d] = %d\n", i, j, byte_read);
close(fd);
}
printf("\n");
}
exit(0);
}
}
output if I enter n = 2 for a 2d array = {{1,2,3},{4,5,6}}. the result is 4 no matter what input values I enter, what's going wrong here?
Enter a number:2
child0 PID: 31930
2 * A[0,0] = 4
Final matrix elements:
A[0,0] = 4
A[0,1] = 4
A[0,2] = 4
A[1,0] = 4
A[1,1] = 4
A[1,2] = 4