added guard for empty expressions

src/ee.c

@@ -11,8 +11,13 @@ main (const int argc, const char* argv[])
     const char** endPtr = argv+argc,
               ** arg    = argv+1   ;
 
+    /* Guard for empty expressions */
+    if (arg>=endPtr) {
+        error |= ERR_NO_EXPR;
+    }
+
     char* fmt = "%g\n";
-    if (strcmp(*arg,"-f") == 0) {
+    if (!error && strcmp(*arg,"-f") == 0) {
         fmt ="%f\n";
         arg+= 1;
     }
@@ -35,11 +40,14 @@ main (const int argc, const char* argv[])
 
     }
 
+    /* Detect malformed expressions */
+    if (!error) {
         if (expr == NULL)
             error |= ERR_NS_OPERANDS;
 
         else if ((*expr).tail != NULL)
             error |= ERR_NS_OPERATORS;
+    }
 
     report(&expr, fmt);
 
@@ -202,6 +210,8 @@ report(STACK* expr, char* fmt)
     else if (error & ERR_DIV_BY_ZERO)
         printf("Undefined\n");
 
+    else if (error & ERR_NO_EXPR)
+        printf("No expression provided.\n");
     else
         printf(fmt, peek(expr));
 }

src/ee.h

@@ -11,6 +11,7 @@ const int ERR_NS_OPERATORS      = 2;
 const int ERR_INVALID_INPUT     = 4;
 const int ERR_INVALID_FACTORIAL = 8;
 const int ERR_DIV_BY_ZERO       = 16;
+const int ERR_NO_EXPR           = 32;
 
 
 struct EE_STACK_NODE {