If condition in C: Getting the average from a given list of input with variation

#include<stdio.h>

main()
{

int a, input[1000];
int choice;
int num,max,low;
double total=0,average;
int array[1000];

clrscr();

  start:
  clrscr();

  printf("\n                  ******** MENU **********\n");
  printf(" [1] Input as many numbers as the user like and ends getting of numbers when -1 is inputted.\n");
  printf(" [2] Getting the largest, lowest and average in a list of numbers.\n");
  printf(" Enter choice : ");
  scanf("%d", &choice);

       if(choice==1)
{
   clrscr();
   for(a=0;a<1000;a++)
      {
      printf("Enter number : ");
      scanf("%d",&input[a]);
    if(input[a]==-1)
      {
      goto start;
      getch();
      }
      }
 }


    if(choice==2)
{
clrscr();

 printf("Enter number of list :");
 fflush(stdin);
 scanf("%d",&num);

     for(a=0;a<num;a++)
{
printf("Enter number:");
scanf("%d",&array[a]);
if (a==0)
{
max=array[a];
low=array[a];
}

if(array[a]>max)
  max=array[a];
if(array[a]<low)
   low=array[a];
total+=array[a];
}
    average=total/num;
    fflush(stdout);
    printf("LOWEST  = %d.\n",low);
    printf("LARGEST = %d.\n",max);
    printf("AVERAGE = %lf.\n",average);


     }


getch();
return 0;
}