C++ MessageBox() and showing interger variables

I am trying to use messagebox() like msgbox(), but harder then I think. I have tried many variations online, but not actually show me the values

int var1 = 10

int var2 = 20

I want to have the message box show the two values along with text explaining which number is showing

sudocode

showstring = 'Variable 1 ' & var1 & ' variable 2 ' & var2

messagebox(NULL, showstring)

How do I go about doing this? Any links or code would be helpful - Thanks

EDIT

Update title to reflect that this is a function for C++