diff --git a/big-int/src/bigint.hpp b/big-int/src/bigint.hpp
index 9d8f030..94fb571 100644
--- a/big-int/src/bigint.hpp
+++ b/big-int/src/bigint.hpp
@@ -33,6 +33,13 @@
 
 namespace libbig
 {
+// sign = 1: positive number
+// sign = 0: negative number
+// flip if its reverse
+
+constexpr bool NEGATIVE = 0;
+constexpr bool POSITIVE = 1;
+
 class largeInt
 {
   private:
@@ -125,7 +132,7 @@ class largeInt
     bool operator!=(int);
     bool operator!=(int64_t);
 
-    bool operator<(largeInt);
+    bool operator<(const largeInt&);
     bool operator<(int);
     bool operator<(int64_t);
     bool operator<(long long);
@@ -150,4 +157,4 @@ class largeInt
 };
 } // namespace libbig
 
-#endif
\ No newline at end of file
+#endif
diff --git a/big-int/src/operators/less_than.cpp b/big-int/src/operators/less_than.cpp
index 48d792b..47b8140 100644
--- a/big-int/src/operators/less_than.cpp
+++ b/big-int/src/operators/less_than.cpp
@@ -32,5 +32,40 @@
 
 namespace libbig
 {
-
+  bool largeInt:: operator < (const largeInt& z) {
+    if (this->sign == NEGATIVE) {
+      if (z.sign == POSITIVE){
+        return true;
+      } else if (z.sign == NEGATIVE){
+        if (this->number.length() > z.number.length()){
+          return true;
+        }
+        if (this->number.length() < z.number.length()){
+          return false;
+        }
+        for(int i = 0; i < this->number.length(); i++) {
+          if (this->number[i] < z.number[i]) {
+            return false;
+          }
+        }
+      }
+    } else if (this->sign == POSITIVE) {
+      if (z.sign == NEGATIVE){
+        return false;
+      } else if (z.sign == POSITIVE){
+        if (this->number.length() < z.number.length()){
+          return true;
+        }
+        if (this->number.length() > z.number.length()){
+          return false;
+        }
+        for(int i = 0; i < this->number.length(); i++) {
+          if (this->number[i] > z.number[i]) {
+            return false;
+          }
+        }
+      }
+    }
+    return false;
+  }
 } // namespace libbig