title: Why is the output of the following two statements different?
body: <p>code:</p>
  
  <pre><code> #define f(a,b) a##b
   #define g(a)   #a
   #define h(a) g(a)
  
   main()
   {
        printf("%s\n",h(f(1,2)));  //[case 1]
        printf("%s\n",g(f(1,2)));  //[case 2]
   }
  </code></pre>
  
  <p>output:</p>
  
  <pre><code>12
  f(1, 2)
  </code></pre>
  
  <p><strong>Why is the output not same in both cases?</strong></p>
  
  <p><em>[I understood the concatenation (<code>a##b</code>) and string conversion (<code>#a</code>) <a href="https://stackoverflow.com/questions/1686324/how-does-this-c-code-work/">here</a>, but I did not get why the output is different in both cases.]</em></p>