uva 406 in C

#include<stdio.h>
 #include<math.h>
 #define max 1005
 char prime[max];
 void sieve()
 {
     int i,j;
     prime[0]=1;
     prime[1]=0;
     for(i=2;i<=max;i+=2)
        prime[i]=0;
     for(i=4;i<=max;i+=2)
        prime[i]=1;

     for(i=3;i<=sqrt(max);i+=2){
        for(j=i*i;j<=max;j+=i)
            prime[j]=1;
     }
 }
 int main()
 {
     sieve();
     int i,j,n,c,ara[1000],p,middle,middle_2,p_num,y=1;
     while(scanf("%d %d",&n,&c)==2){
            printf("%d %d:",n,c);

     p=0;
     for(i=0;i<=n;i++){
        if(prime[i]==0)
            ara[p++]=i;
     }

     middle=p/2;

     if(p%2==1){
        if((c*2-1)>p){

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

                printf(" %d",ara[i]);

            }
        }
        else{
        p_num=(c*2-1-1)/2;

        for(j=middle-p_num;j<=middle+p_num;j++){

                printf(" %d",ara[j]);

        }

     }
     }

     else{
            if((c*2)>p){

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

                printf(" %d",ara[i]);

            }
        }
     else{
        middle_2=middle-1;
        p_num=(c*2-2)/2;
        for(j=middle_2-p_num;j<=middle_2;j++)
            printf(" %d",ara[j]);

        for(j=middle;j<=middle+p_num;j++){

            printf(" %d",ara[j]);

        }
     }
     }
     printf("\n\n");

 }
 }