g++-8 -I/usr/local/include -I. -I./imgui -I./MathExpr/MathExpr -I./imgui/examples/libs/gl3w -DLinux -DIMGUI_UNLIMITED_FRAME_RATE -D_NO_DEBUG_HEAP=1 -Wall -std=c++17 -o build/imgui_math ./imgui/imgui.cpp ./imgui/imgui_demo.cpp ./imgui/imgui_draw.cpp ./imgui/imgui_widgets.cpp ./imgui/imgui_impl_glfw.cpp ./imgui/imgui_impl_opengl3.cpp ./imgui/examples/libs/gl3w/GL/gl3w.c ./main.cpp -lGL -lGLU   -L./MathExpr -lmathexpr

./main.cpp:40:1: error: ‘RVar’ does not name a type; did you mean ‘char’?
 RVar *xvar;
 ^~~~
 char
./main.cpp:41:1: error: ‘RVar’ does not name a type; did you mean ‘char’?
 RVar* vararray[1];
 ^~~~
 char
./main.cpp:42:1: error: ‘ROperation’ does not name a type
 ROperation *op;
 ^~~~~~~~~~
./main.cpp: In function ‘double Func(double)’:
./main.cpp:138:6: error: ‘op’ was not declared in this scope
  y = op->Val();
      ^~
./main.cpp: In function ‘void ElaborateFunction()’:
./main.cpp:147:2: error: ‘xvar’ was not declared in this scope
  xvar = new RVar("x", &funx);
  ^~~~
./main.cpp:147:2: note: suggested alternative: ‘char’
  xvar = new RVar("x", &funx);
  ^~~~
  char
./main.cpp:147:13: error: expected type-specifier before ‘RVar’
  xvar = new RVar("x", &funx);
             ^~~~
./main.cpp:148:2: error: ‘vararray’ was not declared in this scope
  vararray[0] = xvar;
  ^~~~~~~~
./main.cpp:148:2: note: suggested alternative: ‘va_arg’
  vararray[0] = xvar;
  ^~~~~~~~
  va_arg
./main.cpp:149:2: error: ‘op’ was not declared in this scope
  op = new ROperation(function, 1, vararray);
  ^~
./main.cpp:149:11: error: expected type-specifier before ‘ROperation’
  op = new ROperation(function, 1, vararray);
           ^~~~~~~~~~

nm Math.exe | grep RVar
000000000047ed83 T _Z11IsolateVarsRPciPP4RVariPP9RFunction
000000000047ef61 T _Z14IsolateNumbersRPciPP4RVariPP9RFunction
000000000047e967 T _Z5IsVarPKciiPP4RVar
0000000000480e48 T _ZeqRK4RVarS1_
000000000047f130 T _ZN10ROperationC1EPciPP4RVariPP9RFunction
000000000047caa4 T _ZN10ROperationC1ERK4RVar
000000000047f130 T _ZN10ROperationC2EPciPP4RVariPP9RFunction
000000000047caa4 T _ZN10ROperationC2ERK4RVar
000000000047bb70 T _ZN4RVarC1EPKcPd
000000000047bb24 T _ZN4RVarC1ERKS_
000000000047bb70 T _ZN4RVarC2EPKcPd
000000000047bb24 T _ZN4RVarC2ERKS_
000000000047bbac T _ZN4RVarD1Ev
000000000047bbac T _ZN4RVarD2Ev
000000000047c05c T _ZN9RFunctionC1ERK10ROperationiPP4RVar
000000000047bf94 T _ZN9RFunctionC1ERK10ROperationP4RVar
000000000047c05c T _ZN9RFunctionC2ERK10ROperationiPP4RVar
000000000047bf94 T _ZN9RFunctionC2ERK10ROperationP4RVar
0000000000481016 T _ZNK10ROperation10ContainVarERK4RVar
00000000004817e4 T _ZNK10ROperation10SubstituteERK4RVarRKS_
000000000048198a T _ZNK10ROperation4DiffERK4RVar