Added division by zero detection

src/ee.c

@@ -1,4 +1,4 @@
-    #include "ee.h"
+#include "ee.h"
 int error = 0;
 void printStack(STACK);
 
@@ -75,6 +75,11 @@ arrity(const char query)
            0;
 }
 
+bool
+isDivByZero(double *_operands)
+{
+    return _operands[0] == 0;
+}
 
 double
 evaluate(STACK* target_stack, char operator)
@@ -107,6 +112,9 @@ evaluate(STACK* target_stack, char operator)
             break;
 
         case '/' :
+            if (isDivByZero(_operands))
+                error |= ERR_DIV_BY_ZERO;
+            else
                 value = _operands[1] / _operands[0];
             break;
 
@@ -187,6 +195,9 @@ report(STACK* expr, char* fmt)
     else if (error & ERR_INVALID_FACTORIAL)
         printf("Error: Factorials are only supported for positive integers.\n");
 
+    else if (error & ERR_DIV_BY_ZERO)
+        printf("Undefined\n");
+
     else
         printf(fmt, peek(expr));
 }

src/ee.h

@@ -1,5 +1,6 @@
 #include <stdio.h>
 #include <stdlib.h>
+#include <stdbool.h>
 #include <math.h>
 #include <ctype.h>
 #include <string.h>
@@ -9,6 +10,7 @@ const int ERR_NS_OPERANDS       = 1;
 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;
 
 
 struct EE_STACK_NODE {