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 839595d..48dac3f 100644
--- a/k&r/04-funcs-and-prog-struct/04-calc.c
+++ b/k&r/04-funcs-and-prog-struct/04-calc.c
@@ -23,7 +23,7 @@
 #define POP_PRINT_F  "pop -> %.8g\n"
 #define PEEK_PRINT_F "peek -> %.8g\n"
 #define INITIAL_PROMPT_F \
-    "A simple calculator using polish notation.\n" \
+    "A simple polish notation calculator.\n" \
     "Type 'help' for a list of available commands\n" \
     PROMPT_F
 
@@ -38,7 +38,7 @@ double val[MAXVAL];
 #define length() sp
 /* push: push f onto value stack */
 #define push(x) \
-    ((sp < MAXVAL) ? val[sp++] = x : printerr(FULL_STACK_ERR,  (double) (x)))
+    ((sp < MAXVAL) ? val[sp++] = x : printerr(FULL_STACK_ERR, (double) (x)))
 /* pop: pop and return top value from stack */
 double pop(void)
 {
@@ -114,8 +114,8 @@ void print_vars(void)
 /* commutative operator */
 #define COMM_OP(OP) push(pop() OP pop()) 
 /* non-commutative operator */
-#define NONC_OP(OP, T, ...) \
-    do { T op = pop(); __VA_ARGS__ push(((T) pop()) OP op); } while (0)
+#define NONC_OP(OP, ...) \
+    do { double op = pop(); __VA_ARGS__ push(pop() OP op); } while (0)
 /* unary function */
 #define UNARY_FUN(F) push(F(pop()))
 /* unary function with tests */
@@ -124,9 +124,10 @@ void print_vars(void)
 /* commutative function */
 #define COMM_FUN(F) push(F(pop(), pop()))
 /* non-commutative function */
-#define NONC_FUN(F, T, ...) \
-    do { T op = pop(); __VA_ARGS__ push(F(pop(), op)); } while (0)
+#define NONC_FUN(F, ...) \
+    do { double op = pop(); __VA_ARGS__ push(F(pop(), op)); } while (0)
 
+/* OPERAND TESTS */
 /* nonzero operand */
 #define NONZ_SND_OP if (!op) printerr(ZERODIV_ERR); else
 /* operator in range */
@@ -149,31 +150,33 @@ void print_vars(void)
     X(help, "print all available commands", COMMAND) \
     X(vars, "print defined variables and their values", CALL, print_vars, COMMAND)
 
+#define MOD(x, y) ((int) (x) % (int) (y))
+
 #define OPERATORS \
     X(+, "add operands", COMM_OP) \
     X(*, "multiply operands", COMM_OP) \
-    X(-, "substact operands", NONC_OP, double) \
-    X(/, "divide operands", NONC_OP, double, NONZ_SND_OP) \
-    X(%, "modulo operands", NONC_OP, int, NONZ_SND_OP) \
-    X(>, "greater than", NONC_OP, double) \
-    X(<, "less than", NONC_OP, double) \
-    X(<=, "less than or equal", NONC_OP, double) \
-    X(>=, "greater than or equal", NONC_OP, double) \
+    X(-, "substact operands", NONC_OP) \
+    X(/, "divide operands", NONC_OP, NONZ_SND_OP) \
+    X(%, "apply modulo to operands", CALL, MOD, NONC_FUN, NONZ_SND_OP) \
+    X(>, "greater than", NONC_OP) \
+    X(<, "less than", NONC_OP) \
+    X(<=, "less than or equal", NONC_OP) \
+    X(>=, "greater than or equal", NONC_OP) \
     X(==, "test equality", COMM_OP)
 
 #define MATH_H_BINDINGS \
     X(sin, "sine", UNARY_FUN) \
     X(cos, "cosine", UNARY_FUN) \
     X(tan, "tangent", UNARY_FUN) \
-    X(acos, "arc cosine", UNARY_T_FUN, double, IN_RANGE(-1, 1)) \
-    X(asin, "arc sine", UNARY_T_FUN, double, IN_RANGE(-1, 1)) \
+    X(acos, "arc cosine", UNARY_T_FUN, IN_RANGE(-1, 1)) \
+    X(asin, "arc sine", UNARY_T_FUN, IN_RANGE(-1, 1)) \
     X(atan, "arc tangent", UNARY_FUN) \
     X(exp, "exponentional function", UNARY_FUN) \
-    X(log, "natural logarithm", UNARY_T_FUN, double, NON_NEG) \
-    X(log10, "logarithm of base 10", UNARY_T_FUN, double, NON_NEG) \
-    X(log2, "logarithm of base 2", UNARY_T_FUN, double, NON_NEG) \
-    X(pow, "power function", NONC_FUN, double) \
-    X(sqrt, "square root", UNARY_T_FUN, double, NON_NEG) \
+    X(log, "natural logarithm", UNARY_T_FUN, NON_NEG) \
+    X(log10, "logarithm of base 10", UNARY_T_FUN, NON_NEG) \
+    X(log2, "logarithm of base 2", UNARY_T_FUN, NON_NEG) \
+    X(pow, "power function", NONC_FUN) \
+    X(sqrt, "square root", UNARY_T_FUN, NON_NEG) \
     X(ceil, "round up value", UNARY_FUN) \
     X(floor, "round down value", UNARY_FUN) \
     X(round, "round to nearest", UNARY_FUN) \