Added a delete function that lets you delete numbers entered.

demos/calc.cpp

@@ -14,7 +14,7 @@ using std::string, std::wstring;
 
 enum class Event {
   NUMBER, ADD, SUB, MUL,
-  DIV, CLR, NEG, EQ, PUSH, DUP
+  DIV, CLR, NEG, EQ, PUSH, DUP, DEL
 };
 
 const std::unordered_map<string, wstring> LABELS {
@@ -25,7 +25,7 @@ const std::unordered_map<string, wstring> LABELS {
     {"btn8", L"8"}, {"btn9", L"9"}, {"mul", L"*"},
     {"sub", L"-"}, {"add", L"+"}, {"neg", L"±"},
     {"div", L"/"}, {"eq", L"="},
-    {"push", L"^"}, {"pop", L"v"} };
+    {"push", L"^"}, {"pop", L"v"}, {"del", L"DEL"}};
 
 const std::unordered_map<wchar_t, Event> EVENTS {
   {L'0', Event::NUMBER}, {L'1', Event::NUMBER},
@@ -37,7 +37,7 @@ const std::unordered_map<wchar_t, Event> EVENTS {
     {L'+', Event::ADD}, {L'/', Event::DIV},
     {L'C', Event::CLR}, {L'^', Event::PUSH},
     {L'±', Event::NEG}, {L'v', Event::DUP},
-    {L'=', Event::EQ} };
+    {L'=', Event::EQ}, {L'D', Event::DEL}};
 
 
 struct Calculator {
@@ -93,6 +93,11 @@ struct Calculator {
       case ADD: do_op(ADD); break;
       case SUB: do_op(SUB); break;
       case DIV: do_op(DIV); break;
+      case DEL:
+        if(input.size() > 0) {
+          input.pop_back();
+        }
+        break;
       case CLR:
         input = L"";
         stack.clear();
@@ -142,7 +147,7 @@ struct CalculatorUI {
         "[btn7|btn8|btn9]"
         "[btn4|btn5|btn6]"
         "[btn1|btn2|btn3]"
-        "[neg |btn0|_   ]");
+        "[neg |btn0|del]");
   }
 
   void init() {