Frequency table in C++

Question

This is what I have so far; I am trying to have an array with probability of all chars and space in a text file, but I have a problem with the data type.

int main()
{
float x[27];
unsigned sum = 0;
struct Count {
    unsigned n;
    void print(unsigned index, unsigned total) {

        char c = (char)index;
        if (isprint(c)) cout << "'" << c << "'";
        else cout << "'\\" << index << "'";
        cout << " occured " << n << "/" << total << " times";
        cout << ", propability is " << (double)n / total << "\n";
    }
    Count() : n() {}
} count[256];
ifstream myfile("C:\\text.txt"); // one \ masks the other
while (!myfile.eof()) {
    char c;
    myfile.get(c);
    if (!myfile) break;
    sum++;
    count[(unsigned char)c].n++;
}
for (unsigned i = 0; i<256; i++)
{
    count[i].print(i, sum);
}
x[0] = count[33];
int j=68;
 for(int i=1;i<27;i++)
 {
     x[i]=count[j];
     j++;
 }
return 0;
}

Answer 1

#include <iostream>
#include <fstream>
#include <cctype>    
using namespace std;

double probabilities[256]; // now it can be accessed by Count

int main()
{
  unsigned sum = 0;
  struct Count {
    unsigned n;
    double prob;
    void print ( unsigned index, unsigned total ) {
      // if ( ! n ) return;
      probabilities[index] = prob = (double)n/total;
      char c = (char) index;
      if ( isprint(c) ) cout << "'" << c << "'";
      else cout << "'\\" << index << "'";
      cout<<" seen "<<n<<"/"<<total<<" times, probability is "<<prob<<endl;
    }
    Count(): n(), prob() {}
    operator double() const { return prob; }
    operator float() const { return (float)prob; }
  } count[256];
  ifstream myfile("C:\\text.txt"); // one \ masks the other
  while(!myfile.eof()) {
    char c;
    myfile.get(c);
    if ( !myfile ) break;
    sum++;
    count[(unsigned char)c].n++;
  }
  for ( unsigned i=0; i<256; i++ ) count[i].print(i,sum);
  return 0;
}

I incorporated various changes suggested - Thanks!

Now, who finds the 4 ways to access the actual probabilities?

Answer 2

you are allocating a buffer with size 1000000 1 million characters.

char file[1000000] = "C:\text.txt";

This is not good as the extra values in the buffer are not guaranteed to be zero, the can be anything.

For Windows to read a file you need something like this. I will not give you the solution, you need to learn using msdn and documentation to understand this fully::

you need to include the #include <windows.h> header from the SDK first.

Look at this example here: http://msdn.microsoft.com/en-us/library/windows/desktop/aa363778(v=vs.85).aspx

this example as appending a file to another. Your solution will be similar, instead of writing list to other file, process the buffer to increment your local variables and update the state of the table.

Do not set a large number you come up with for the buffer, as there will risk of not enough buffer space, and thus overflow. You should do like example:

• read some bytes in buffer
• process that buffer and increment the table

• repeat until you reach end of file

  while (ReadFile(hFile, buff, sizeof(buff), &dwBytesRead, NULL) && dwBytesRead > 0) { // write you logic here }