关于void

#include<iostream>
#include<cmath>
#include<cstdio>
using namespace std;

long A[100010],n;
long k1,k2;

long sep(int x,int y,int k)
{
	int mid = x + (y-x)/2;
	long i = x,j = y,key = A[mid];
	A[mid] = A[x];
	while(i < j)
	{
		while(i < j && A[j] >= key)
		  j--;
		A[i] = A[j];
		while(i < j && A[i] < key)
		  i++;
		A[j] = A[i];
	}
	A[i] = key;
	if(i == k) return A[i];
	if(i > k) sep(x,i-1,k);
	else if(i < k) sep(i+1,y,k);
}

/*bool*/void prime()
{
	int m = k2 - k1;
	if(m < 2)
	{
		printf("NO\n");
		return;
	}
	else if(m == 2)
	{
		printf("YES\n");
		printf("%d\n", m);
		return ;
	}
	else if(m > 2)
	{
		for(int i = 2; i <= int(sqrt(m))+1; i++)
		  if(m%i == 0)
		  {
		  	printf("NO\n");
			printf("%d\n", m);
		  	return ;
		  }
		printf("YES\n");
		printf("%d\n", m);
		return;
	}
/*	int i;
	if(m<=1) return false;
	for(i=2; i*i<=m; i++)
	  if(m%i==0)
	    return false;
    return true;*/
}

int main()
{
	int k,i;
	cin>>n>>k;
	for(i = 1; i <= n; i++)
	  cin>>A[i];
	k1 = sep(1,n,k);
	k2 = sep(1,n,n-k+1);
	prime();
/*	int m = k2 - k1;
	if(prime())
	  printf("YES\n");
	else
	  printf("NO\n");
	printf("%d\n", m);*/
	return 0;
}

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void输出是否会有溢出？若在wikioi上，注释部分可AC，而在void函数内输出则WA