diff --git a/src/midend/SysYIRGenerator.cpp b/src/midend/SysYIRGenerator.cpp
index 2e0e910..50c4114 100644
--- a/src/midend/SysYIRGenerator.cpp
+++ b/src/midend/SysYIRGenerator.cpp
@@ -262,10 +262,12 @@ void SysYIRGenerator::compute() {
   }
   
   // 弹出BinaryExpStack的表达式
-  while(begin < end) {
+  int count = end - begin;
+  for (int i = 0; i < count; i++) {
     BinaryExpStack.pop_back();
-    BinaryExpLenStack.back()--;
-    end--;
+  }
+  if (!BinaryExpLenStack.empty()) {
+    BinaryExpLenStack.back() -= count;
   }
 
   // 计算后缀表达式