Update c.html.markdown

c.html.markdown

@@ -472,7 +472,22 @@ char c[] = "This is a test.";
 str_reverse(c);
 printf("%s\n", c); // => ".tset a si sihT"
 */
-
+//as we can return return only one variable
+//to change values of more than one variables we use call by reference
+void swapTwoNumbers(int *a, int *b)
+{
+int temp = *a;
+*a = *b;
+*b = temp;
+}
+/*
+int first = 10;
+int second = 20;
+printf("first: %d\nsecond: %d\n", first, second);
+swapTwoNumbers(&first, &second);
+printf("first: %d\nsecond: %d\n", first, second);
+// values will be swapped
+*/
 // if referring to external variables outside function, must use extern keyword.
 int i = 0;
 void testFunc() {