Binarysearch

#include<stdio.h>
#include<malloc.h>
int Binsearch(int a[],int N,int whichnumber)
{
    int low, high, mid,j;
     j = -1;
    low = 0;
    high = N-1;
    while ((low <= high)&&(j == -1))
    {
        mid = (low + high)/2;
        if (a[mid] == whichnumber)  j = mid+1;
        else if (a[mid] > whichnumber)  high = mid - 1;
        else low = mid + 1;
    }
    return j;
}
int main()
{
    int N,M;
    int *a;
    char *b;
    int i;
    printf("Please input the number of the array : ");
    scanf("%d ",&N);
    a = (int*)malloc(N*sizeof(int));
    for (i = 0; i < N; i++)
        scanf("%d", &a[i]);
        
    int where,whichnumber;
    printf("Please input which number would you want to find :");
    scanf("%d", &whichnumber);
    where = Binsearch(a, N, whichnumber);
    if (where==-1)
    {
       printf("error!");
    }
    else
    printf("%d",where);
}