diff --git a/lib.nas b/lib.nas
index 4565162..f73afbd 100644
--- a/lib.nas
+++ b/lib.nas
@@ -144,4 +144,19 @@ var math=
     isnan: func(x)  {return __builtin_isnan(x);  }
 };
 
-var D2R=math.pi/180;
\ No newline at end of file
+var D2R=math.pi/180;
+var FPS2KT=0.5925;
+var FT2M=0.3048;
+var GAL2L=3.7854;
+var IN2M=0.0254;
+var KG2LB=2.2046;
+var KT2FPS=1.6878;
+var KT2MPS=0.5144;
+var L2GAL=0.2642;
+var LB2KG=0.4536;
+var M2FT=3.2808;
+var M2IN=39.3701;
+var M2NM=0.00054;
+var MPS2KT=1.9438;
+var NM2M=1852;
+var R2D=180/math.pi;
\ No newline at end of file
diff --git a/main.cpp b/main.cpp
index 8f21d52..da72a77 100644
--- a/main.cpp
+++ b/main.cpp
@@ -46,7 +46,7 @@ void logo()
 void die(const char* stage,std::string& filename)
 {
     std::cout<<"["<<stage<<"] in <"<<filename<<">: error(s) occurred,stop.\n";
-    exit(1);
+    std::exit(1);
     return;
 }
 
diff --git a/nasal_builtin.h b/nasal_builtin.h
index 4b443b1..b98f5a8 100644
--- a/nasal_builtin.h
+++ b/nasal_builtin.h
@@ -351,10 +351,7 @@ nasal_ref builtin_int(std::vector<nasal_ref>& local_scope,nasal_gc& gc)
 {
     nasal_ref val_addr=local_scope[1];
     if(val_addr->type!=vm_num)
-    {
-        builtin_err("int","\"value\" must be number");
-        return nullptr;
-    }
+        return gc.nil_addr;
     int number=(int)val_addr->ptr.num;
     nasal_ref ret_addr=gc.gc_alloc(vm_num);
     ret_addr->ptr.num=(double)number;
@@ -364,10 +361,7 @@ nasal_ref builtin_num(std::vector<nasal_ref>& local_scope,nasal_gc& gc)
 {
     nasal_ref val_addr=local_scope[1];
     if(val_addr->type!=vm_str)
-    {
-        builtin_err("num","\"value\" must be string");
-        return nullptr;
-    }
+        return gc.nil_addr;
     nasal_ref ret_addr=gc.gc_alloc(vm_num);
     ret_addr->ptr.num=val_addr->to_number();
     return ret_addr;
diff --git a/stl/lib.nas b/stl/lib.nas
index 4565162..f73afbd 100644
--- a/stl/lib.nas
+++ b/stl/lib.nas
@@ -144,4 +144,19 @@ var math=
     isnan: func(x)  {return __builtin_isnan(x);  }
 };
 
-var D2R=math.pi/180;
\ No newline at end of file
+var D2R=math.pi/180;
+var FPS2KT=0.5925;
+var FT2M=0.3048;
+var GAL2L=3.7854;
+var IN2M=0.0254;
+var KG2LB=2.2046;
+var KT2FPS=1.6878;
+var KT2MPS=0.5144;
+var L2GAL=0.2642;
+var LB2KG=0.4536;
+var M2FT=3.2808;
+var M2IN=39.3701;
+var M2NM=0.00054;
+var MPS2KT=1.9438;
+var NM2M=1852;
+var R2D=180/math.pi;
\ No newline at end of file