Transform the Expression (ONP) problem

[vuanh]

this is my code for this problem:

#include<iostream>
#include<string.h>
using namespace std;
int len;
char s[10000],out[1000];
int xuat(int a)
{
	int t1=0,t2=0,i;
	if ((s[a]!='(')and (s[a]!=')')) 
	{	
		if ( (s[a]!='+') and (s[a]!='-') and  (s[a]!='*') and (s[a]!='/') and (s[a]!='^' )) {out[a]=s[a];} 
			else
			{	if (s[a+2]==')') {out[a+2]=s[a];}	
					else	 {						
								for (i=a+1;i<=len;i++)
									{
										if (s[i]=='(') {t1=t1+1;} else 
                                                                                                                       { if(s[i]==')')
                                                                                                                                        { t2=t2+1;}
                                                                                                                        }
										if (t1==t2) {out[i+1]=s[a];return 0;}
									}	
							}
			}
	}
	return 0;
}
int main()
{
	int n,i,j,v;
	cin>>n;
	for (i=1;i<=n;i++)
	{	cin>>s;
		len=strlen(s);
		for (v=0;v<=2*len;v++) {out[v]='0';}
		for (j=0;j<=len;j++)  	// xet tung phan tu cua chuoi
		{
			xuat(j);     		// ham xet phan tu vi tri j
		}
		for (v=0;v<=(2*len);v++) { if (out[v]!='0') {cout<<out[v];}}
		cout<<endl;
	}
	return 0;
}

i check all Example problem, all its are correct
but after submit , error: wrong answer. please held me.