diff --git a/k&r/04-funcs-and-prog-struct/04-calc.c b/k&r/04-funcs-and-prog-struct/04-calc.c
index 80e6f31..c290c25 100644
--- a/k&r/04-funcs-and-prog-struct/04-calc.c
+++ b/k&r/04-funcs-and-prog-struct/04-calc.c
@@ -69,10 +69,13 @@ double lst_print;
 char var_flags[NS_SIZE];
 double var_vals[NS_SIZE];
 
+/* is_var: return 0 if c is not a variable name */
+#define is_var(c) isalpha(c)
+
 /* set_var: pop val from stack, set variable c to val */
 #define set_var(c) \
     do { \
-        int i = c - 'a'; \
+        int i = tolower(c) - 'a'; \
         var_flags[i] = 1; \
         var_vals[i] = pop(); \
     } while (0)
@@ -80,13 +83,21 @@ double var_vals[NS_SIZE];
 /* get_var: push value of c to stack */
 #define get_var(c) \
     do { \
-        int i = c - 'a'; \
+        int i = tolower(c) - 'a'; \
         if (!var_flags[i]) \
             printerr(VAR_NOT_SET_ERR, i+'a'); \
         else \
             push(var_vals[i]); \
     } while (0)
 
+/* print_vars: print all set variables and their values */
+void print_vars(void)
+{
+    int i;
+    for (i = 0; i < NS_SIZE; i++)
+        if (var_flags[i])
+            printf("%c = %.8g\n", i+'a', var_vals[i]);
+}
 
 /* --------- CALCULATOR FUNCTION TYPES */
 /* the following macros allow us to call native c constructs 
@@ -132,6 +143,7 @@ double var_vals[NS_SIZE];
     X(swap, "swap top two elements of stack", COMMAND) \
     X(clear, "clear stack", COMMAND) \
     X(help, "print all available commands", COMMAND) \
+    X(vars, "print defined variables and their values", CALL, print_vars, COMMAND)
 
 #define OPERATORS \
     X(+, "add operands", COMM_OP) \
@@ -204,8 +216,8 @@ int main()
         TOKENS
     #undef X
     #define X(C, DESC, F) \
-        if (t_len == 2 && token[0] == C && isalpha(token[1])) \
-            F(tolower(token[1])); \
+        if (t_len == 2 && token[0] == C && is_var(token[1])) \
+            F(token[1]); \
         else
         VAR_TOKENS
     #undef X