how to use code written in C++ console form written in C in windows form application C++ [code works in console]

I have written a program in C that works in c++ console . Now i drew the interface i want it look like. but I cant combine this code with code needed in windows form application C++. Do i have to know C++ or C is enough like in console app? For ex, i have 

scanf( "%19s ", string1);  

this means that i have to type a word max lenth 19 in console , but what if i want it to read from the textBox1?

and do the calculation

printf ("%d\n" , sum);

 and pot the answer into textBox2.
i prepared visual form of my future program but i just need to combine C code to this Win form app. 

the problem is that i don't know c++ i write in C..