Thread: tolower error

Originally Posted by dwks

That's right. It was just another solution. I thought that perhaps the OP would like to see how transform() works.

Looking inside the STL headers can be tremendously informative. All kinds of cool, inspiring stuff in there.

Yes, I figured that out eventually . . . sorry, I edited it out because I thought no one would have had time to read it. Evidently someone did.

I saw it only by accident

Errors:
C:/Dev-Cpp/include/ctype.h: In function `std::string string_lower(const std::string&)':
C:/Dev-Cpp/include/ctype.h:63: error: too few arguments to function `int tolower(int)'
main.cpp:17: error: at this point in file

C:/Dev-Cpp/include/c++/3.4.2/bits/stl_algo.h: In function `_OutputIterator std::transform(_InputIterator, _InputIterator, _OutputIterator, _UnaryOperation) [with _InputIterator = __gnu_cxx::__normal_iterator<const char*, std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, _OutputIterator = std::back_insert_iterator<std::string>, _UnaryOperation = int]':
main.cpp:17: instantiated from here
C:/Dev-Cpp/include/c++/3.4.2/bits/stl_algo.h:789: error: `__unary_op' cannot be used as a function

I'm getting annoyed :P

Can you post your latest code?

Code:

#include <iostream>
#include <cctype>
#include <iterator>
#include <algorithm>

using namespace std;

string string_lower(const string &str)
{
       class lower
       {
             public:
                    char operator()(char ch) { return tolower(ch); }
       };

   string x;
   transform(str.begin(), str.end(), back_inserter(x), std::tolower());
   return x;
}

int main(int argc, char *argv[])
{
    //Alla våra svenska ord i en array
    string swedish[2];
    swedish[0] = "hej";
    swedish[1] = "vem";
    
    //Alla våra engelska ord i en array
    string english[2];
    english[0] = "hi";
    english[1] = "who";
    
    /*Alla ord ska ligga i ordning så att swedish[2] representerar det svenska ordet för english[2]*/
    //Precis XD
    
    string insert; //Namnet på stringen som användaren skriver in i
    int quantity = 3; //Hur många ord det finns + 1. Om det finns 2 frågor ska det vara 3 här. Om det är 4 frågor ska det vara 5 här.
    int done = 0; //Hur många ord som har blivit svarade
    int points = 0; //Hur många poäng man får
    
    //Skriver ut en text
    cout << "Här kommer du få svenska ord som du ska översätta!\nDå börjar vi!\n\n\n";
    
    //Kör en while-sats för att alla ord ska vara med
    while (done < quantity) 
    {
          cout << "Vad heter " << swedish[done] << " på engelska?\n"; //Skriver ut vad heter lala beronde på vilket ord det är
          cin >> insert; //Låter användaren skriva in ett ord
          
          string lower = string_lower(swedish[done]); //Gör alla bokstäver små
          
          if (english[done] == lower) //kollar om det är rätt
          {
                     points = points + 1; //Lägg till 1 poäng
          } 
    done++;
    }
    
    cout << "Du fick " << points << " poäng!";
}

Don't put the parentheses on std::tolower.

I realize the parentheses are confusing. The reason for the difference is that std::tolower is a FUNCTION, which can serve directly as the functor of the transform. On the other hand, the hand-cooked lower class is not a function, but a CLASS. When you INSTANTIATE the class (using the () after the name, which is a constructor call), you get an OBJECT which acts as a functor.

When you add the () to the end of std::tolower(), you actually CALL the function. This function returns an int, so the transform() call is getting passed an integer as a functor, which is invalid.

You should also #include <string> since you are using the string class.

Still gets an error:
18 C:\Users\Fredrik\Desktop\main.cpp no matching function for call to `transform(__gnu_cxx::__normal_iterator<const char*, std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, __gnu_cxx::__normal_iterator<const char*, std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::back_insert_iterator<std::string>, <unknown type>)'

Code:

Code:

#include <iostream>
#include <cctype>
#include <iterator>
#include <algorithm>
#include <string>

using namespace std;

string string_lower(const string &str)
{
       class lower
       {
             public:
                    char operator()(char ch) { return tolower(ch); }
       };

   string x;
   transform(str.begin(), str.end(), back_inserter(x), tolower);
   return x;
}

int main(int argc, char *argv[])
{
    //Alla v&#229;ra svenska ord i en array
    string swedish[2];
    swedish[0] = "hej";
    swedish[1] = "vem";
    
    //Alla v&#229;ra engelska ord i en array
    string english[2];
    english[0] = "hi";
    english[1] = "who";
    
    /*Alla ord ska ligga i ordning s&#229; att swedish[2] representerar det svenska ordet f&#246;r english[2]*/
    //Precis XD
    
    string insert; //Namnet p&#229; stringen som anv&#228;ndaren skriver in i
    int quantity = 3; //Hur m&#229;nga ord det finns + 1. Om det finns 2 fr&#229;gor ska det vara 3 h&#228;r. Om det &#228;r 4 fr&#229;gor ska det vara 5 h&#228;r.
    int done = 0; //Hur m&#229;nga ord som har blivit svarade
    int points = 0; //Hur m&#229;nga po&#228;ng man f&#229;r
    
    //Skriver ut en text
    cout << "H&#228;r kommer du f&#229; svenska ord som du ska &#246;vers&#228;tta!\nD&#229; b&#246;rjar vi!\n\n\n";
    
    //K&#246;r en while-sats f&#246;r att alla ord ska vara med
    while (done < quantity) 
    {
          cout << "Vad heter " << swedish[done] << " p&#229; engelska?\n"; //Skriver ut vad heter lala beronde p&#229; vilket ord det &#228;r
          cin >> insert; //L&#229;ter anv&#228;ndaren skriva in ett ord
          
          string lower = string_lower(swedish[done]); //G&#246;r alla bokst&#228;ver sm&#229;
          
          if (english[done] == lower) //kollar om det &#228;r r&#228;tt
          {
                     points = points + 1; //L&#228;gg till 1 po&#228;ng
          } 
    done++;
    }
    
    cout << "Du fick " << points << " po&#228;ng!";
}

I got Dev-C++ and it wont work