minor tweaks to simplify code

Author: fsaadatmand

Diff for: chapter04/4-4.c

@@ -2,6 +2,7 @@
  * Exercise 4-4. Add commands to print the top element of the stack without
  * popping, to duplicate it, and to swap the top two elements. Add command to
  * clear the stack.
+ *
  * By Faisal Saadatmand
  */
 
@@ -13,7 +14,6 @@
 #define NUMBER  '0'          /* signal that a number was found */
 #define MAXVAL  100          /* max depth of val stack */
 #define BUFSIZE 100
-#define TOP     val[sp - 1]  /* top element in stack */
 
 /* functions */
 int    getop(char []);
@@ -31,7 +31,6 @@ int    sp;                   /* next free stack position */
 double val[MAXVAL];          /* value stack */
 char   buf[BUFSIZE];         /* buffer from ungetch */
 int    bufp;                 /* next free position in buf */
-int    peak;                 /* flag to peak at top of the stack */
 
 /* push: push f onto value stack */
 void push(double f)
@@ -103,19 +102,18 @@ void ungetch(int c)
 /* printTOP: print top of the stack without pop */
 void printTOP(void)
 {
-	if (sp < 1)
-		printf("stack empty\n");
-	printf("\t%.8g\n", TOP);
+	double top;
+
+	top = pop();
+	printf("\t%.8g\n", top);
+	push(top);
 }
 
 /* duplicateTop: duplicate the top element in the stack */
 void duplicateTop(void)
 {
 	double top;
 
-	if (sp < 1)
-		return;
-
 	push(top = pop());
 	push(top);
 }
@@ -125,24 +123,12 @@ void duplicateTop(void)
  {
 	 double top1, top2;
 
-	 if (sp < 2) {
-		 if (sp == 1)
-			 printf("error: 1 element in stack\n");
-		 return;
-	 }
 	 top1 = pop();
 	 top2 = pop();
 	 push(top1);
 	 push(top2);
 }
 
-/* clear: clears the entire stack */
-void clearStack(void)
-{
-	while (sp > 1)
-		pop();
-}
-
 /* reverse Polish Calculator */
 int main(void)
 {
@@ -179,24 +165,17 @@ int main(void)
 			else
 				printf("error: zero divisor\n");
 			break;
-		case '!':
-			peak = 1;
+		case '?':
+			printTOP();
 			break;
-		case '#':
+		case 'd':
 			duplicateTop();
 			break;
-		case '&':
+		case 's':
 			swapTopTwo();
 			break;
-		case '~':
-			clearStack();
-			break;
 		case '\n':
-			if (peak) {
-				printTOP();
-				peak = 0;
-			} else
-				printf("\t%.8g\n", pop());
+			printf("\t%.8g\n", pop());
 			break;
 		default:
 			printf("error: unknown command %s\n", s);