How to properly use the stdarg.h library in C and does it work with WSL?

Question

C++ / C#

I continue my thorny path of learning C. I ran into the question of the need to write a function with the possibility of accepting a non-regular number of variables.
By assignment, it must use the stdarg.h library. But I can't understand how it works. I've read several articles that describe the principle in a very clear way... And in practical application, I go into a blunt. Whether the described principle is not true, tol and I do not understand something. When I try to get a value, instead of the expected one, I get a nonsense of characters, letters and numbers. I'm trying to use everything on WSL Ubuntu.
What am I doing wrong?
To try to understand the principle, I implemented a mock code:

spoiler

#include <stdio.h>
#include <stdarg.h>

int main(char fmt, ...)
{
    va_list ap;
    char c;
    char *s;

    c = fmt;
    va_start(ap, fmt);
    while (1)
    {
    if (c == 'c')
    	{
      printf("make c\n");
      c = (char)va_arg(ap, int);
    		printf("%c\n", c);
      break ;
    }
    if (c == 's')
    	{
      printf("make s\n");
      s = va_arg(ap, char *);
    		printf("%s\n", s);
      break ;
    }
    printf("not eat!\n");
    break ;
  }
    va_end(ap);
    return (0);
}

Answer 1

With main it doesn't work that way. The main signature with command line arguments looks like this:

int main(int argc, char **argv) {
}

Whatever is the equivalent of your code. Main is passed a pointer to an array of strings, but your code assumes that all arguments will be passed on the stack. Because of this, nothing works.