Fibonacci series

This function accepts the number of terms in the Fibonacci sequence in the child process, creates an array, and redirects the output to the parent via pipe. Parent must wait till the child develops the Fibonacci series. The received text always displays -1, although the transmitted text displays the number of entered numbers *4, which is acceptable.

#include<stdio.h>
#include<unistd.h>
#include<sys/types.h>
#include<string.h>

int* fibo(int n)
{
    int* a=(int*)malloc(n*sizeof(int));
    *(a+0)=0;
    *(a+1)=1;
    int i;
    for(i=0;i<n-2;i++)
    {
        *(a+i+2)=*(a+i)+(*(a+i+1));
    }
    return a;
    }


    int main()
    {
        int* fib;
        int fd[2];
        pid_t childpid;
        int n,nb;

        int k=pipe(fd);
        if(k==-1)
        {
        printf("Pipe failed");
        return 0;
    }

    childpid=fork();
    if(childpid == 0) 
    {
        printf("Enter no. of fibonacci numbers");
        scanf("%d",&n);
        fib=fibo(n);
        close(fd[0]);
        nb=(fd[1],fib,n*sizeof(int));
        printf("Sent string: %d \n",nb);
        exit(0);
    }
    else
    {
        wait();
        close(fd[1]);
        nb= read(fd[0],fib,n*sizeof(int));
        printf("Received string: %d ",nb);
    }
    return 0;
}