From f4528e64b95f55c3cff0b94ef42ecfe88e4874ff Mon Sep 17 00:00:00 2001
From: Vera Lewis <vera.lewis@xenami.net>
Date: Thu, 25 Dec 2025 20:25:58 -0600
Subject: [PATCH] added guard for empty expressions

---
 src/ee.c | 20 +++++++++++++++-----
 src/ee.h |  1 +
 2 files changed, 16 insertions(+), 5 deletions(-)

diff --git a/src/ee.c b/src/ee.c
index 16229d1..ddcd50d 100644
--- a/src/ee.c
+++ b/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[])
 
     }
 
-    if (expr == NULL)
-        error |= ERR_NS_OPERANDS;
+    /* Detect malformed expressions */
+    if (!error) {
+        if (expr == NULL)
+            error |= ERR_NS_OPERANDS;
 
-    else if ((*expr).tail != NULL)
-        error |= ERR_NS_OPERATORS;
+        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));
 }
diff --git a/src/ee.h b/src/ee.h
index 77faa9b..09f9c8f 100644
--- a/src/ee.h
+++ b/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 {