title: invalid assignment operator Error on add , subtract, divide, multiply signs
body: <p>I am getting the invalid assignment error when trying to parse two strings and them perform mathematical operations on them :S</p>
  
  <p>the error is in this line,    </p>
  
  <pre><code>                   IfirstValue+IfirstValue;
  </code></pre>
  
  <p>Here is the complete code,</p>
  
  <pre><code>firstValue = 34;
      secondValue = 10;
  
       IfirstValue = Integer.parseInt(firstValue);
                 IsecondValue = Integer.parseInt(secondValue);
  
                     if (operator == 3){
                         IfirstValue+IfirstValue;
                     }
  </code></pre>
  
  <p>I tried replacing '+' by '-' , '/' , '*' but the error remains same :S</p>
  
  <p>(operator is input from the user)</p>
  
  <p>please explain why it is happening.</p>