Snake Case vs Camel Case

int issnakecase(string inputstring)
{
   int i;

   for(i=0;inputstring[i]!='\0';i++)
   {

     if((inputstring[i]>=97 && inputstring[i]<=122) || inputstring[i]==95)
     {
         if(inputstring[i]==95 && inputstring[i+1]==95)
             return 0;
     }
     else
     { return 0;}

   }

   if(inputstring[0]=='_' || inputstring[i-1]=='_')
   {
       return 0;
   }
       return 1;
}

int iscamelcase(string inputstring)
{
   int i;
   for(i=0;inputstring[i]!='\0';i++)
   {
     if((inputstring[i]>=65 && inputstring[i]<=90) || (inputstring[i]>=97 && inputstring[i]<=122))
     {}
       else
       { return 0;}

     }

    if(inputstring[0]>=65 && inputstring[0]<=90)
    {
        return 0;
    }

  return 1;
}

string switchCase(string S) {
string inputstring=S;
  string outputstring;


  int i,j=0;
  if(issnakecase(inputstring) == 1)
  {
      //cout<<"Snake Case";
    for(i=0;inputstring[i]!='\0';i++)
    {

       if(inputstring[i]>=97 && inputstring[i]<=122)
      {
         // outputstring[j]=inputstring[i];
          outputstring.push_back(inputstring[i]);
         //  cout<<"Small letter"<<outputstring[j]<<"----";
       }
        else
       {
          i++;
          outputstring.push_back(inputstring[i]-32);
            //outputstring[j]=inputstring[i]-32;
          // cout<<"underscore"<<outputstring[j]<<"---";
        }
    j++;
   }
    }
  else if(iscamelcase(inputstring)==1)
 {
      //cout<<"Camel Case";
     for(i=0;inputstring[i]!='\0';i++)
     {
        if(inputstring[i]>=97 && inputstring[i]<=122)
        {
            outputstring.push_back(inputstring[i]);
        }
        else
        {
          outputstring.push_back('_');
          outputstring.push_back(inputstring[i]+32);
        }
      j++;
     }

}

  else
  {
   outputstring = "ERROR";
  }
  return outputstring;
}