Thread: Help with Converting between letters and numbers using arrays...

I think i've got it but not too sure, and If anyone knows any other way to do this how could i do it?

Code:

#include<iostream>
#include<cctype>
#include<string>
#include<fstream> 
#include<iomanip>
using namespace std;
  
char integer_to_letter(int);
int letter_to_integer(char);
void print_header();

int main(int argc, char *argv[])
{
   const int SIZE = 26;
   int freq[SIZE] = {0};
   char letter;
   int index;
   ifstream fin(argv[1]);
   ofstream fout(argv[2]);
   print_header();
   fin >> letter;
   while(!fin.eof())
     {
     if(isalpha(letter))
       {
       index = letter_to_integer(tolower(letter));
       freq[index]++;
       }
     fin >> letter;
     }
   fout << "Count the occurances of letters in a file" << endl
	<< "producing a frequency" << endl << endl
	<< "letter freq           letter freq" << endl
	<< "------ -------------- ------ ---------------" << endl;
   for(int i = 0; i < 13; i++)
     {
     char one = integer_to_letter(i);
     tolower(one);
     char two = integer_to_letter(i+13);
     tolower(two);
     fout << right << setw(6) << one << left << " "
	  << setw(15) << freq[i] << " "
	  << right << setw(6) << two << " "
	  << left << freq[(i+13)] << endl;
     }
   fin.close();
   fout.close();
   return 0;
}

/*
 * Name: letter_to_integer
 * Purpose: Convert a letter to the corresponding number
 * Receive: Data from a file
 * Return: Number corresponding to the letter
 */
int letter_to_integer(char letter)
{
  int index = (letter - 'a');
  return index;
}

/*
 * Name: integer_to_letter
 * Purpose: Convert a number to the corresponding letter
 * Receive: Data from a file
 * Return: Letter corresponding to the number
 */
char integer_to_letter(int index)
{
  return(static_cast<char>('a' + index));
}

/*
 * Name: print_header
 * Purpose: Display header
 * Receive: Nothing
 * Return: Header
 */
void print_header()
{
  cout << "\n";
  cout << "\n";
  cout << "\n";
}

Explanation: Tolower will return the ASCII value for the lowercase equivalent of the ASCII character chr, if it is a letter.

...and the question still stands: what do those lines do? Try this Welshy:

Code:

char ch = 'A';
tolower(ch);
cout<<ch<<endl;

and you'll see what I mean.