title: CommandLine Java Calculator
body: <p>I've just learned java but from my old experience coming from C++ i tought that i can write a commandline calculator wich supports all 4 basic operators with just one line. But i am having a bit of problem.</p>
  
  <p>This is my code:</p>
  
  <pre><code>import java.util.Scanner;
  
  public class omg {
      public static void main(String args[]) {
          int fnum,snum,anum = 0;
          String strtype; //The original calculation as string
          char[] testchar; //Calculation as chararray
          char currentchar; //current char in the char array for the loop
          int machinecode = 0; //Operator converted to integer manually
          String tempnumstr; //first and second numbers temp str to be converted int
          int operatorloc = 0; //operator location when found
          char[] tempnum = new char[256];
          Scanner scan = new Scanner(System.in); // The scanner obviously
          System.out.println("Enter The Calculation: ");
          strtype = scan.nextLine();
          testchar = strtype.toCharArray(); //converting to char array
          for(int b = 0; b &lt; testchar.length; b++) //operator locating
          {
              currentchar = testchar[b];
              if(currentchar == '+') {
                  machinecode = 1;
                  operatorloc = b;
              }
              else if(currentchar == '-') {
                  machinecode = 2;
                  operatorloc = b;
              }
              else if(currentchar == '*') {
                  machinecode = 3;
                  operatorloc = b;
              }
              else if(currentchar == '/') {
                  machinecode = 4;
                  operatorloc = b;
              }
          }
          for(int t = 0;t &lt; operatorloc;t++) { //transferring the left side to char
              tempnum[t] = testchar[t];
          }
              tempnumstr = tempnum.toString(); //converting char to string
              fnum = Integer.parseInt(tempnumstr); //parsing the string to a int
          for(int temp = operatorloc;temp &lt; testchar.length;temp++) { //right side
              for(int t = 0;t&lt;(testchar.length-operatorloc);t++) {
                  tempnum[t] = testchar[temp];
              }
          }
          tempnumstr = tempnum.toString(); //converting to char
          snum = Integer.parseInt(tempnumstr); //converting to int
          switch(machinecode) { //checking the math to be done
          case 1:
              anum = fnum + snum;
              break;
          case 2:
              anum = fnum - snum;
              break;
          case 3:
              anum = fnum * snum;
              break;
          case 4:
              anum = fnum / snum;
          }
          System.out.println(anum); //printing the result
      }
  }
  </code></pre>
  
  <p>This is my code but when i run it it will ask me the calculation and then give this error.</p>
  
  <pre><code>Exception in thread "main" java.lang.NullPointerException
      at omg.main(omg.java:38)
  </code></pre>
  
  <p>There might be a better and easier way of doing this i would like to hear both a better way and a fix for my way. Thanks in advance</p>