这种全部RE段错误要怎么解决？

 #include<bits/stdc++.h>
using namespace std;

int now,tail=0,opt,n,x,temp;
int heap[30010];

void put(int k){
	heap[++tail]=k;
	now=tail;
	while(now>1){
		if(heap[now]>heap[now>>1])return;
		
		temp=heap[now];
		heap[now]=heap[now>>1];
		heap[now>>1]=temp;
		
		now=now>>1;
	}
}

int pop(){
	int res=heap[1];
	heap[1]=heap[tail--];
	now=1;
	
	while((now<<1)<=tail){
		int next=now<<1;
		if (next<tail && heap[next+1]<heap[next])next++;
		if(heap[now]<heap[next])return res;
		
		temp=heap[now];
		heap[now]=heap[next];
		heap[next]=temp;
		
		now=next;
	}
}

int main()
{
	scanf("%d",&n);
	while(n--){
		scanf("%d",&opt);
		if(opt==1){scanf("%d",&x);put(x);}
		if(opt==2){printf("%d\n",heap[1]);}
		if(opt==3){pop();}
	}
	return 0;
}