Wrong anti-spam code

Formulation

The function a_capital modifies the string by turning each character a into A. The code below has the implementation of the function. It is missing only one line in the main function. The main function declares the string w and reads the string from the user input. The missing line should call the function a_capital in such a way that every character a in w is turned into A. Write the command that should be placed instead of // ??? // to achieve the described outcome.

#include<iostream>
void a_capital(std::string* s){
   long len=(*s).length();
   for(long i=0;i<len;++i){
      if((*s)[i]=='a'){
         (*s)[i]='A';
      }
   }
}
int main(){
   std::string w;
   std::cin>>w;
   // ??? //
   std::cout<<w<<"\n";
   return 0;
}

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