Trouble with an array method in a class

#include <string>
#include <cctype>
#include <iostream>
#include <fstream>
#include <cmath>
using namespace std;
 
const int NUMBER_OF_LETTERS = 26;  //A-Z
const int NUMBER_OF_LANGUAGES = 4;
 
const double INTERPRET[NUMBER_OF_LANGUAGES][NUMBER_OF_LETTERS]=
       {{8.27,1.48,2.94,4.03,11.78,2.22,1.72,6.77, //engelska
         7.39,0.12,0.81,3.76,2.85,6.71,7.79,1.54,
         0.05,5.95,6.69,9.07,2.66,1.13,2.14,0.19,
         1.89,0.03},
        {7.97,1.40,3.55,3.79,16.89,1.02,1.00,0.75, //franska
         7.08,0.38,0.04,5.51,2.82,8.11,5.19,2.78,
         1.01,6.69,8.35,7.22,6.09,1.35,0.02,0.54,
         0.30,0.15},
        {9.50,1.11,1.53,5.30,8.94,1.74,3.57,3.94,  //svenska
         3.98,0.89,3.26,4.93,3.41,8.46,5.01,1.77,
         0.00,6.73,5.56,9.20,1.94,2.42,0.00,0.05,
         0.45,0.00},
        {5.12,1.95,3.57,5.07,16.87,1.35,3.00,5.79, //tyska
         8.63,0.19,1.14,3.68,3.12,10.64,1.74,0.42,
         0.01,6.30,6.99,5.19,3.92,0.77,1.79,0.01,
         0.69,1.24}};
 
class Text
{
private:
  string text ;
  int letters ;
  int other ;
  int n[NUMBER_OF_LETTERS] ;
public:
  Text() ; 
  void setText ( string nyText ) ; 
  int calcAbs () ;
  void writeAbs () ;
  void absToRel ( int numb[], double histRel[] ) ;
  void plotRel ( double histRel[] ) ;
  string interpret ( double histRel[] ) ;
} ;
// -------------------------------------------------------
// Functions
// -------------------------------------------------------
 
void file_name (string &in_file) ;
void read (string &in_file, string &out_string) ;
 
// -------------------------------------------------------
// Main program
// -------------------------------------------------------
 
int main()
{
  string text ;
  int numb ;
  Text myText ;
  
  string in_file ;
  string out_string = "" ;
  int prob_lang = 99 ;
  string lang[4] = {"Eng", "Fre", "Swe", "Ger"} ;
 
  cout << "Type the name of the file:" << endl ;
  
  file_name (in_file) ;
 
  read (in_file, out_string) ;
 
  myText.setText ( text ) ;
 
  numb = myText.calcAbs () ;
  myText.writeAbs () ;
  myText.absToRel () ; // Here is error 2193
  myText.plotRel () ;  // Here is error 2193
  
  cout << "The most probebly language is: " << 
  lang[prob_lang] << endl ;
 
  return 0;
}
// -------------------------------------------------------
// Class implementation
// -------------------------------------------------------
Text::Text ()
{
}
// -------------------------------------------------------
void Text::setText ( string newText ) 
{
  text = newText ;
}
// -------------------------------------------------------
int Text::calcAbs ()
// This method calculates the number of letters in the text
{  
  letters = other = 0 ;
 
  for (int i=0; i<(int) text.length(); i++)
  {
    if (isalpha(text.at(i))) letters++ ;
    else other++ ;
  }
  
  cout << "Number of letters in the text is: " << letters << endl ;
 
  for (int i = 0; i < NUMBER_OF_LETTERS; i++ )
       n[i] = 0 ;
  
  for (int i = 0; i < (int) text.length(); i++)
  {
    int index ;
    
    if (text.at(i) >= 'a' && text.at(i) <= 'z')
    {
      index = text.at(i) - 'a'; n[index]++ ;
    }
    if (text.at(i) >= 'A' && text.at(i) <= 'Z')
    {
	    index = text.at(i) - 'A'; n[index]++ ;
    }
  }
  return letters ;
} 
// -------------------------------------------------------
void Text::writeAbs () 
// This method prints the number of letters and the letter in to columns
{
  cout << "\nLetter\tFrekvence\n" ;
  for (int i = 0; i<NUMBER_OF_LETTERS; i++)
    {
      char b = char (i+'A') ;
      if (n[i]>0) cout << b << "\t" << n[i] << endl ;
    }
}
// --------------------------------------------------------
void Text::absToRel ( int numb[], double histRel[] )
// This method should calculate the histogram
{
  double percent = 100 ;
  
  for (int i = 0; i < NUMBER_OF_LETTERS; i++)
  {
    histRel[i] = ((double)numb[i]/(double)letters) * percent ;
  }
}
// --------------------------------------------------------
void Text::plotRel (double histRel[])
// This method plots the histogram
{ 
  cout << "The frekvence of each letter is:" << endl ;
  for (int i = 0; i < NUMBER_OF_LETTERS; i++)
  {
    if (histRel[i]>=0)
    {
      char b = char (i+'A') ;
      
      string s = "" ; 
 
      for (int c = 0; c < (int)histRel[i]; c++)
        s += "**" ;
      
      if ((histRel[i] - (int)histRel[i]) >= 0.5)
        s += "*";
      
      cout << b << "\t" << s << endl ;     
    }    
  }
}
// --------------------------------------------------------
string Text::interpret ( double histRel[] )
// This method should compare the histogram with the four langugages and give the most probeble language.
{
  string lang[4] = {"Eng", "Fra", "Swe", "Ger"};
  double diff ;
  double square_sum_save = 999999999.0 ;
  int prob_lang = 99 ;
  
  //Comparing the different langugages
  cout << "\nLanguage\tSquare sum\n" << endl ;
  for (int s=0; s<NUMBER_OF_LANGUAGES; s++)
  {
    double square_sum_all = 0.0 ;
    for (int i=0; i<NUMBER_OF_LETTERS; i++)
	 {
	   diff = INTERPRET[s][i] - histRel[i];
	   square_sum_all += diff*diff; //kvadratskillnad
	 }
    cout << lang[s] << "\t" << square_sum_all << endl ;
  }
  
  //To find the most probable language
  for (int s=0; s<NUMBER_OF_LANGUAGES; s++)
  {
    double square_sum = 0.0 ;
    for (int i=0; i<NUMBER_OF_LETTERS; i++)
    {          
      diff = INTERPRET[s][i] - histRel[i];
      square_sum += diff*diff;
    } 
    if (square_sum < square_sum_save)
    {
      square_sum_save = square_sum ;
      prob_lang = s ;
    }
  }
    //cout << square_sum_save << endl ;
    //cout << "The most probable language is: " << lang[prob_lang] 
    //<< endl ; 
    return lang[prob_lang] ;    
}
// --------------------------------------------------------
// The functions
// --------------------------------------------------------
// Checking the in file
void file_name (string &in_file)
{
  string file_ending = ".txt" ;
  
  cout << "Type the name of the file: " << endl ;
  getline ( cin, in_file ) ;
 
  if (in_file.rfind(file_ending) != in_file.length() - 4)
    in_file.append (file_ending) ;
}
// --------------------------------------------------------
// Reading the file
void read (string &in_file, string &out_string)
{
  string in_row ;
 
  ifstream fin ( in_file.c_str() ) ;
   
  if ( !fin )   //Felkontroll
  {  
    cout << "The file doesn't exist" << endl ;
    exit ( EXIT_FAILURE ) ;
  } 
 
//Saving the file row by row
  while ( getline (fin, in_row) )
  {
    out_string.append(in_row) ;
    out_string.append("\n") ; 
  } 
}

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