diff --git a/rpn.c b/rpn.c
--- a/rpn.c
+++ b/rpn.c
@@ -11,6 +11,7 @@ double val;
 
 extern double pop(void);
 extern void push(double);
+extern void clear(void);
 
 extern int getsym(void);
 
@@ -53,6 +54,9 @@ int main(void)
 		case 'd':
 			pop();
 			break;
+		case 'C':
+			clear();
+			break;
 		default:
 			fprintf(stderr, "Unknown '%c'\n", sym);
 			return 1;
diff --git a/stack.c b/stack.c
--- a/stack.c
+++ b/stack.c
@@ -19,3 +19,8 @@ double pop(void)
 {
 	return stack[top--];
 }
+
+void clear(void)
+{
+	top = -1;
+}