title: C program to solve expressions with functions in it
body: <p>I tried to write a program some thing like a expression solver to support only the following functions</p>
  
  <pre><code>length();
  substr();
  concat();
  </code></pre>
  
  <p>Hence if the user inputs </p>
  
  <pre><code>concat('Int Part : ', substr(5.00+4.00, 0, 1))
  </code></pre>
  
  <p>the output should be</p>
  
  <pre><code>Int Part : 9
  </code></pre>
  
  <p>Is there any library to do this or is there any place I can learn how to do this kind of thing.</p>