Remove characters from alphanumeric string

PROBLEM :

Remove all characters from an alphanumeric string.

Input:
The first line of the input contains T denoting the number of testcases. First line of each test case will be an alphanumeric string.

Output:
 For each test case output will be a numeric string after removing all the characters.

Constraints:
1 <= T <= 30
1 <= size of string <= 100

Example:

Input:
1
AA123BB4

Output:
1234

--------------------------------------------------------------------------------
SIMPLE c++ IMPLEMENTATION :
--------------------------------------------------------------------------------

#include<iostream>
using namespace std;
#include<string.h>
int main()
 {
int t,i,j,l ;
char str[100] ;
cin>>t ;
while(t--)
{
   scanf(" %[^\n]s",str) ;
   l=strlen(str) ;
   j=0 ;
 
   for(i=0;i<l;i++)
   {
       if(!((str[i]>='A'&&str[i]<='Z')||(str[i]>='a'&&str[i]<='z')))
       {
           str[j]=str[i] ;
           j++ ;
       }
   }
   str[j]='\0' ;
 
   cout<<str<<endl ;
}
return 0;
}

---------------------------------------------------------------------------------