为什么编译失败？

#include<cstdio>
#include<iostream>
#include<cstring>
using namespace std;
int ans=0;
int main()
{
//	freopen("t.in","r",stdin);
//	freopen("t.out","w",stdout);
	char s[10];
	gets(s);
	int n=strlen(s);
	for(int i=0;i<n;i++)
	{
		if(s[i]>='a' && s[i]<='z') ans++;
		if(s[i]>='A'&&s[i]<='Z') ans++;
		if(s[i]>='0'&&s[i]<='9') ans++;
	}
	cout<<ans;
	return 0;	
}