revise answer

Author: fsaadatmand

chapter04/4-14.c

@@ -1,35 +1,45 @@
 /*
  * Exercise 4-14. Define a macro swap(t, x, y) that interchanges two arguments
  * of type t. (Block structure will help).
+ *
  * By Faisal Saadatmand
  */
 
 #include <stdio.h>
 
-#define SWAP(t, x, y) if (sizeof(x) == sizeof(t) && sizeof(y) == sizeof(t)) \
-{t temp = (x); temp = (x), (x) = (y), (y) = temp;}
+#define SWAP(t, x, y) if (sizeof((x)) == sizeof(t) && sizeof((y)) == sizeof(t)) \
+{t temp = ((x)); ((x)) = ((y)), ((y)) = temp;}
 
-/* simpler but no type check */
-/*
-#define SWAP(t, x, y) if (x != y) {t temp = (x); temp = (x), (x) = (y), (y) = temp;}
-*/
-
-/* alternatively we can use bitwise XOR, though it is considered bad practice */
-/*
-#define SWAP(t, x, y) if (sizeof(x) == sizeof(t) && sizeof(y) == sizeof(t)) \
-{(x) ^= (y), (y) ^= (x), (x) ^= (y);}
+ /*
+ * Alternatively we could use bitwise XOR for the swap, but it is considered
+ * bad practice. 
+ *
+ * 	#define SWAP(t, x, y) if (sizeof((x)) == sizeof(t) && sizeof((y)) == sizeof(t)) \
+ * 	{(x) ^= (y), (y) ^= (x), (x) ^= (y);}
 */
 
 int main(void)
 {
-	int a = 6;
-	int b = 3;
+	int a = 6, b = 3;
+	char c = 99; /* 'c' */
+	float f = 42.0f ;
+	long int l = 25;
 
-	printf("Before SWAP a = %i b = %i\n", a, b);
+	printf("int and int: types match\n");
+	printf("Before SWAP\n a = %i b = %i\n", a, b);
+	SWAP(int, a, b);
+	printf("After  Swap\n a = %i b = %i\n", a, b);
 
+	printf("\nchar and float: types don't match\n");
+	printf("Before SWAP\n a = %c b = %2f\n", c, f);
 	SWAP(int, a, b);
+	printf("After  Swap\n a = %c b = %2f\n", c, f);
 
-	printf("After  Swap a = %i b = %i\n", a, b);
+	printf("\nlong and int: types don't match,\
+ but implicit conversion takes place\n");
+	printf("Before SWAP\n a = %i b = %li\n", a, l);
+	SWAP(int, a, b);
+	printf("After Swap\n a = %i b = %li\n", a, l);
 
 	return 0;
 }