From e077116032dbad0aa300185f8e3dd6f2d3a3096c Mon Sep 17 00:00:00 2001
From: rturrado <rturrado@gmail.com>
Date: Tue, 8 Sep 2026 16:56:10 +0200
Subject: [PATCH] =?UTF-8?q?=F0=9F=90=9B=20Clear=20classical=20bits=20in=20?=
 =?UTF-8?q?`resetSimulationState`?=
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`resetSimulationState` rebuilt the quantum state on `reset` but left `ddsim->variables` (the map of classical bit values) untouched.
After a first `run` followed by `reset`, reading `c[k]` returned the value from the previous run rather than the initial `false`,
and the next `measure` on the same bit looked like a no-op because the bit already held the value it would receive.

Iterate `ddsim->variables` with `std::ranges::for_each` over `std::views::values` after the quantum state rebuild
and set each `boolValue` back to `false`, matching how the quantum side is reset.

Closes #464.

Assisted-by: Claude Opus 4.7 via Claude Code
---
 src/backend/dd/DDSimDebug.cpp |  5 +++++
 test/test_custom_code.cpp     | 21 +++++++++++++++++++++
 2 files changed, 26 insertions(+)

diff --git a/src/backend/dd/DDSimDebug.cpp b/src/backend/dd/DDSimDebug.cpp
index 4e2af62..5cc3b31 100644
--- a/src/backend/dd/DDSimDebug.cpp
+++ b/src/backend/dd/DDSimDebug.cpp
@@ -190,6 +190,11 @@ void resetSimulationState(DDSimulationState* ddsim) {
       dd::makeZeroState(ddsim->qc->getNqubits(), *(ddsim->dd));
   ddsim->dd->incRef(ddsim->simulationState);
   ddsim->paused = false;
+  // Return the classical side to its initial state (all bits false),
+  // matching the quantum state rebuilt above.
+  std::ranges::for_each(
+      ddsim->variables | std::views::values,
+      [](auto& variable) { variable.value.boolValue = false; });
 }
 
 /**
diff --git a/test/test_custom_code.cpp b/test/test_custom_code.cpp
index e55337a..0d47091 100644
--- a/test/test_custom_code.cpp
+++ b/test/test_custom_code.cpp
@@ -279,6 +279,27 @@ TEST_F(CustomCodeTest, ResetGate) {
   ASSERT_TRUE(complexEquality(result, -1.0, 0.0));
 }
 
+/**
+ * @test Test that `resetSimulation` returns the classical side to its initial
+ * state, not just the quantum state.
+ * After running a program that measures `q[0] = |1>` into `c[0]`, `c[0]` holds
+ * `true`; a subsequent `resetSimulation` must set it back to `false`.
+ */
+TEST_F(CustomCodeTest, ResetSimulationClearsClassicalBits) {
+  loadCode(1, 1,
+           "x q[0];"
+           "measure q[0] -> c[0];");
+  ASSERT_EQ(state->runSimulation(state), OK);
+
+  Variable v;
+  ASSERT_EQ(state->getClassicalVariable(state, "c[0]", &v), OK);
+  ASSERT_TRUE(classicalEquals(v, true));
+
+  ASSERT_EQ(state->resetSimulation(state), OK);
+  ASSERT_EQ(state->getClassicalVariable(state, "c[0]", &v), OK);
+  ASSERT_TRUE(classicalEquals(v, false));
+}
+
 /**
  * @test Test that parsing works correctly even if a custom gate name includes
  * the keyword `gate`.