使用stack来模拟结果就WA了一个checkpoint

#include<iostream>
#include<stack>
#include<cstring>
using namespace std;
stack<char> cardA,cardB,cardC;
char card[110],s;

void mvA(void)
{
	s=cardA.top();
	cardA.pop();
	return;
}
void mvB(void)
{
	s=cardB.top();
	cardB.pop();
	return;
}
void mvC(void)
{
	s=cardC.top();
	cardC.pop();
	return;
}
int main()
{
	int l;
    scanf("%s",card);
    l=strlen(card);
    for(int i=0;i<=l-1;i+=1) cardA.push(card[i]);
    scanf("%s",card);
    l=strlen(card);
    for(int i=0;i<=l-1;i+=1) cardB.push(card[i]);
    scanf("%s",card);
    l=strlen(card);
    for(int i=0;i<=l-1;i+=1) cardC.push(card[i]);
    mvA();
    while(1)
    {
    	if(cardA.empty())
    	{
    		cout<<"A"<<endl;
    		return 0;
		}
		else if(cardB.empty())
    	{
    		cout<<"B"<<endl;
    		return 0;
		}
		else if(cardC.empty())
    	{
    		cout<<"C"<<endl;
    		return 0;
		}
    	if(s=='a') mvA();
    	else if(s=='b') mvB();
    	else if(s=='c') mvC();
	}
    
	
}

https://atcoder.jp/contests/abc045/submissions/44191240