Pythagors into java-code (i got the idea, i think, but need it simplified)

Question

Goodday all :),
I have been trying to turn the forumula | a^2 + b^2 = c^2 | into java code.
To clear it up a little more;
1. Define unknown variable
2. Define values of other two variables
3. Program calculates
x1. unkown variable is 'a'
x2. b = 20 , c = 40
x3. a = [(40^2) - (20^2)] ^0.5 (sorry couldnt figure out superscript)
What i was thinking as a concept;
1. Java asks for uknown value -> user defines as 'a' , 'b' or 'c'.
2. Java If else statement
2.1 if 'd' -> java asks again
2.2 else 'e' --> java asks again etc (if else statemenst from d - z)
import java.io.*;
public class example {
     public static void main(String[] args) {
          System.out.println("define uknown value");
          BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
          boolean running = true;
          while(running) {
                    String line = reader.readLine();
                    if (line.startsWith("d")) {
                         System.out.println("wrong input, define unknown value");
                         running = true;
                         } else      if (line.startsWith("e")) {
                         System.out.println("wrong input, define unknown value");
                         running = true;
                         } else      if (line.startsWith("f")) {
                         System.out.println("wrong input, define unknown value");
                         running = true;
                         } else      if (line.startsWith("g")) {
                         System.out.println("wrong input, define unknown value");
                         running = true;and furter i was thinking;
If a, b or c is pressed it will ask for the values of the other two
and it will be such a code as above, repeating itself;
                    String line = reader.readLine();
                    if (line.startsWith("a")) {
                         System.out.println("please define b");
                         running = true;
                         if (line.startsWith("1")) {
                         int x = 1;
                         System.out.println("b=1");
                         running = true;
                         } else      if (line.startsWith("2")) {
                         int x = 2;
                         System.out.println("b=2");
                         running = true;
                         } else      if (line.startsWith("3")) {
                         int x = 3;
                         System.out.println("b=3");
                         running = true;and so on till, lets say 1000?
Now my question is;
Is this the right way to make this program?
I would have like a .java file of severel megebytes if i wanted the values to get up to 10000 or something >.<

Answer 1

Aargh! No. This code snippet might be of help.
try {
   int x = Integer.parseInt("42");
   System.out.println("X = " + x);
} catch( NumberFormatException e ) {
   System.err.println("Not a number: " + e);
   e.printStackTrace();
}You would probably also find it useful to read about "regular expressions" if you always expect the formula to have exactly the same form.