Code:
#include <fstream.h>
#include <stdlib.h>
// Math library
#include <math.h>

const int FileNameLen = 30, ArrayLen = 6;

// The class array
class array 
{
public: 
array(void);
//Inline functions 
inline int getsize() {return(size);}
void read(void);
void write(void);
void     draw(void);
private:

//Private - available only to member functions
int x[ArrayLen];
int size;
};


array::array(void)
{
size = 0;
}

//  Read the array

void array::read(void)
{
size = 0;
// Read each value 
do {
cout << "Enter a value\t?";
cin >> x[size++]; // Read an integer 
} while (x[size-1] != 0 && size < ArrayLen);

// Array indices run from 0 to n-1 
        size = (size == ArrayLen)? size - 2: size - 1;
}


void array::write(void)
{
//CREATE A FILE
ofstream outfile; // file object
char filename[FileNameLen]; // Store the file name
// as a character string
cout << "Enter file name ->\t";
cin >> filename;

// Open the file
outfile.open(filename);
// If you can't open the file, print an error message
// and quit
if (!outfile) {
cerr << "Cannot open " << filename << endl;
exit(1);
}


for (int i = 0;  i < size;  i++) 
outfile << "x[" << i << "] = " << x[i] << '\n';


}

void array::draw(void)
{
ifstream infile; // file object
char filename[FileNameLen]; // Store the file name
char inchar; // as a character string

cout << "Enter file name ->\t";
cin >> filename;

infile.open(filename);

if (!infile) {
cerr << "Cannot open " << filename << endl;
exit(1);
}

//Read the file  a charachter
while (!infile.eof())  
{
inchar = infile.get(); //This reads in 
//even whitespace charachters
cout << inchar; //Display it on screen

} 
infile.close();  //close the file


}



int main(void)
{ 

double sum = 0.0;
double sumOfSquares = 0.0;
double average = 0.0;
double standardDeviation = 0.0;

//display file of screen
const int FileNameLen = 30; // constant integer
ifstream infile;   //file object

average = sum / ArrayLen;
standardDeviation = sqrt(sumOfSquares / ArrayLen - average * average);


array myarray;


myarray.draw();

cout << "\nThe average is: " << average << endl;
cout << "The standard deviation is: " << standardDeviation <<endl;
return(0);
}
also consider that the program reads the following txt file that has these values
x[0] = 5
x[1] = 6
x[2] = 7
x[3] = 45

so the program has to find the average and standard deviation. can someone help me out and show me how is that done? i have the formulas and all but i dont know how to compute all that from the array.