模板

int queue[10010];
int hh=1,tt=0;
void push1(int x)
{
    queue[++tt]=x;
}
void pop1()
{
    if(hh>tt){
        cout<<"ERR_CANNOT_POP"<<endl;
    }
    else
    {
        hh++;
    }
}
int query1()
{
    if(hh>tt){
        cout<<"ERR_CANNOT_QUERY"<<endl;
    }
    return queue[hh];
}
int size1()
{
    return tt-hh+1;
}

例题

题解

#include<iostream>
using namespace std;
int tt = 0,hh = 1;
int a[10010];
void push1(int x)
{
	a[++tt] = x;
}
void pop1()
{
	if(hh>tt) cout<<"ERR_CANNOT_POP"<<endl;
	else hh++;
}
void query1()
{
	if(hh>tt) cout<<"ERR_CANNOT_QUERY"<<endl;
	else cout << a[hh] <<endl;
}
void size1()
{
	cout<<tt-hh+1<<endl;
}
int main()
{
	int n;
	cin >> n;
	for(int i = 1;i<=n;i++)
	{
		int x,y;
		cin >> x;
		if(x == 1)
		{
			cin >> y;
			push1(y);
		}
		if(x == 2)
		{
			pop1();
		}
		if(x == 3)
		{
			query1();
		}
		if(x == 4)
		{
			size1();
		}
	}
	return 0;
}