Blog: CS506 Assignment No. 1 Fall 2011 Solution

Question: 

Write a program that computes the average and standard deviation of the text floating point numbers in a file. Use the following formulas for the average and the standard deviation of N values. The formulas compute the sum, the sum of squares, the average, the average square, the variance, and finally, the standard deviation.

sum = x1 + x2 + x3 + ... + xN-1 + xN 

sumSQ = x12 + x22 + x32 + ... + xN-12 + xN2 

avg = sum/N

avgSQ = sumSQ/N

var = avgSQ - avg2

sd = var(1/2)

The input file will contain any number text floating point numbers, similar to the following:

10.5

12.9

9.67

12.05

8.23

10.08

10.23

7.7

10.4

11.34

Numbers could be several, or none per line, and negative numbers are perfectly OK. 

Solution:

Input Text:

10.0

20.0

30.0

40.0

50.0

............

SAVE THIS FILE IN .JAVA

import java.io.*;

import java.util.*;

import javax.swing.*;

public class assignment1{

public static void main( String args[] ){

try{

FileReader fr = null;

BufferedReader br = null;

fr = new FileReader ("input.txt");

br = new BufferedReader (fr);

String line = br.readLine();

double sum =0 ;

while (line != null) {

double num = Double.parseDouble(line);

sum += num;

line = br.readLine();

}

JOptionPane.showMessageDialog(null, "Sum = " + sum);

br.close();

fr.close();

}

catch(NumberFormatException nfEx) {

System.out.println(nfEx);

}

catch(FileNotFoundException fnfEx){

System.out.println(fnfEx);

}

catch(IOException ioEx){

System.out.println(ioEx);

}

}

}