matrix addition using shared memory

I want to add 2 matrices using shared memory and parallel processes, in linux, but my code doesnt run correctly .
Where is the problem?

#include <stdio.h>

#include <sys/shm.h>

#include <sys/stat.h>

#include <stdlib.h>



int main ()

{



int idA,idB,idC, child_id;

int *A,*B, *C;//the 3 arrays

int* child_memory;

int *pA, *pB, *pC;

const int size = 4096;

int i;

//allocate shared memory for an array of 5 integers

idA = shmget(IPC_PRIVATE, 5*sizeof(int), S_IRUSR | S_IWUSR);

idB = shmget(IPC_PRIVATE, 5*sizeof(int), S_IRUSR | S_IWUSR);

idC = shmget(IPC_PRIVATE, 5*sizeof(int), S_IRUSR | S_IWUSR);



//attach shared memory to parent

A = (int *) shmat(idA, NULL, 0);

B = (int *) shmat(idB, NULL, 0);

C = (int *) shmat(idC, NULL, 0);

for(i=0; i<5; i++){

         A[i]=1;

         B[i]=2;

         C[i]=0;

         }

for (i=0; i<5; i++){

    printf("A[%d]=%d B[%d]=%d  C[%d]=%d\n",i,A[i],i,B[i],i,C[i]);

}

printf("\n"); 

for(i=0;i<5; i++){

   child_id=fork();

   if (child_id==0){

       A = (int*) shmat(idA, NULL, 0);

       B = (int*) shmat(idB, NULL, 0);

       C = (int*) shmat(idC, NULL, 0);             

       C[i] = A[i] + B[i];

       

   }

   else if (child_id>0){

    wait(0);

        

   }

   else {perror("fork");exit(1);}

}   

printf("C[%d] = %d ", i,C[i]);       



shmdt(A);shmdt(B);shmdt(C);



shmctl(idA, IPC_RMID, NULL);

shmctl(idB, IPC_RMID, NULL);

shmctl(idC, IPC_RMID, NULL);

return 0;

}

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