How to output designated command in library or header file

Hi!

First, I’m not good at English. Though it is wrong, please deal leniently because it is hard work to me.

Actually, I want to output korean. But, There is a great diversity of opinion.

So, I try to make custom library or header file. And, input designated command(custom char) in library.

For example, if input A take advantage of my custom library to output ‘가’.

Like this.

#import<cstdio>

int main()
{
    char a;
    scanf("%c", &a);
    if (a=='c') {
        a='z';
    }
}

This is my idea to output language. So, How to output designated command in library or header file?

If you think the good idea for output korean, can you tell me?^^

I need your help. Thank you.