Couple changes to C to close https://github.com/adambard/learnxinyminutes-docs/pull/594

c.html.markdown

@@ -4,6 +4,7 @@ filename: learnc.c
 contributors:
     - ["Adam Bard", "http://adambard.com/"]
     - ["Árpád Goretity", "http://twitter.com/H2CO3_iOS"]
+    - ["Jakub Trzebiatowski", "http://cbs.stgn.pl"]
 
 ---
 
@@ -175,6 +176,9 @@ int main() {
   i2 * i1; // => 2
   i1 / i2; // => 0 (0.5, but truncated towards 0)
 
+  // You need to cast at least one integer to float to get a floating-point result
+  (float)i1 / i2 // => 0.5f
+  i1 / (double)i2 // => 0.5 // Same with double
   f1 / f2; // => 0.5, plus or minus epsilon
   // Floating-point numbers and calculations are not exact
 
@@ -194,9 +198,11 @@ int main() {
   2 >= 2; // => 1
 
   // C is not Python - comparisons don't chain.
-  // WRONG:
-  //int between_0_and_2 = 0 < a < 2;
-  // Correct:
+  // Warning: The line below will compile, but it means `(0 < a) < 2`.
+  // This expression is always true, because (0 < a) could be either 1 or 0.
+  // In this case it's 1, because (0 < 1).
+  int between_0_and_2 = 0 < a < 2;
+  // Instead use:
   int between_0_and_2 = 0 < a && a < 2;
 
   // Logic works on ints