find the diameter of a tree

Here is the program to find the diameter of a binary tree.

int diameter = 0;
int findDiameter(struct tree * node)
{
 int dim ,l_len,r_len;
 /* If null node came then return 0 */
 if(node == 0)
  return 0;
 /* Initialize all the temp length variables by 0 */
 dim = l_len = r_len = 0;
 /* Recursive call for left & right subtree */
 l_len = findDiameter(node->left);
 r_len = findDiameter(node->right);
 /* Calculate the depth at this level */ 
 dim = r_len + l_len + 1;
 /* If the current level diameter is bigger then previous */
 /* Then save the current diameter as biggest one */
 if(dim > diameter)
  diameter = dim;
 /* Return the depth, till current node */
 return (MAX(l_len,r_len) + 1);
}