Manipulate http request

Hi,

I am looking for some info on how i can change the url that is formed by this code It is part of already functioning arduino mega. Currently it creates this url:

192.168.1.158/UserEvent%201,0 HTTP/1.1

i want to replace "UserEvent%20" , with "idx="

and, replace the number after the comma with "On" in case number is 1, and "Off", in case that number after comma is 0

I know that UserEvent%201,0 is stored or referenced by "TempString", so i have to somehow perform magic on TempString....

Could someone point me in the direction how i can do that?

byte SendHTTPEvent(struct NodoEventStruct *Event)
  {
  byte x;

  if(Settings.TransmitHTTP==VALUE_OFF || Settings.HTTPRequest[0]==0)
    return false;

  char *HttpRequest=(char*)malloc(INPUT_LINE_SIZE);
  char *TempString=(char*)malloc(INPUT_LINE_SIZE);
  
  
  Event2str(Event,TempString);
  
   strcat(HttpRequest,TempString);

  free(TempString);
  x=SendHTTPRequest(HttpRequest);
  free(HttpRequest);
  return x;
}

Actually, the significant code is in Event2str(), which you didn't post.