Looks like the brainfuck is working. It can do a hello world program.

game_engine.cpp

@@ -1,5 +1,6 @@
 #include <map>
 #include <string>
+#include <iostream>
 #include <fmt/core.h>
 #include <fmt/color.h>
 #include "game_engine.hpp"
@@ -51,6 +52,53 @@ Brainfucker::Brainfucker() {
 
 }
 
+/*
+ * Just a jank way to use a counter to find
+ * the previous matching brace rather than
+ * using a stack. Should work for now.
+ */
+void Brainfucker::jump_forward() {
+  int counter = 1;
+
+  for(++ip; // when counter hits 0 we found it
+      counter > 0 && ip < code.size();
+      ++ip)
+  {
+    char op = code.at(ip);
+    if(op == '[') {
+      // new branch so increment
+      ++counter;
+    } else if(op == ']') {
+      // close branch so decrement
+      --counter;
+    }
+  }
+
+  ++ip; // need to go 1 after
+}
+
+/*
+ * Same jank style of using a counter to
+ * jump back.
+ */
+void Brainfucker::jump_backward() {
+  int counter = 1;
+
+  for(--ip; // when counter hits 0 we found it
+      counter > 0 && ip > 0;
+      --ip)
+  {
+    char op = code.at(ip);
+    if(op == '[') {
+      // close branch so decrement
+      --counter;
+    } else if(op == ']') {
+      // new branch so increment
+      ++counter;
+    }
+  }
+}
+
 /*
  * Totally fragile but it seems to be working
  * enough to test the idea.
@@ -67,17 +115,31 @@ void Brainfucker::run(int ticks) {
         --dp;
         break;
       case '+':
-        data[dp] = 1;
+        data[dp] = data[dp] + 1;
         break;
       case '-':
-        data[dp] = 0;
+        data[dp] = data[dp] - 1;
         break;
       case '.':
-        print("{}", data.at(dp));
+        cout << (char)data.at(dp);
         break;
       case ',':
         print(ERROR, "Not implemented.\n");
         break;
+      case '[': {
+          // [ - if 0 jump to after ]
+          if(data.at(dp) == 0) {
+            jump_forward();
+          }
+        }
+        break;
+      case ']': {
+        // ] if not 0 jump to after [
+          if(data.at(dp) != 0) {
+            jump_backward();
+          }
+        }
+        break;
       default:
         print(ERROR, "Unknown operation {}\n", op);
     }

game_engine.hpp

@@ -18,6 +18,8 @@ class Brainfucker {
   void run(int count);
   void set_code(string &code);
   void reset();
+  void jump_backward();
+  void jump_forward();
 };
 
 class GameEngine {

tests/game_engine.cpp

@@ -1,7 +1,7 @@
 #include <catch2/catch_test_macros.hpp>
 #include "../game_engine.hpp"
 
-TEST_CASE("brainfuck test", "[brainfuck]") {
+TEST_CASE("basic brainfuck test", "[brainfuck]") {
   Brainfucker bf;
   string code{"+.>+.>+.>"};
 
@@ -23,6 +23,16 @@ TEST_CASE("brainfuck test", "[brainfuck]") {
   REQUIRE(bf.code.empty());
 }
 
+
+TEST_CASE("brainfuck loop test", "[brainfuck]") {
+  Brainfucker bf;
+  // this is a hello world program from wikipedia
+  string code{"++++++++[>++++[>++>+++>+++>+<<<<-]>+>+>->>+[<]<-]>>.>---.+++++++..+++.>>.<-.<.+++.------.--------.>>+.>++."};
+
+  bf.set_code(code);
+  bf.run(code.size());
+}
+
 TEST_CASE("game engine can start and take hit", "[brainfuck]") {
   // test fails on purpose right now
   GameEngine game{4};