I'm implementing printf function in C/Linux

Program:

 #ifndef PRINTF_H
 #define PRINTF_H
 #include "my_put_char.h"

 int my_printf(char *str, ...);

 #endif

This is my Header file for my function.

#include <stdio.h>
#include "my_put_char.h"

void my_put_char(char c) 
{
     fwrite(&c, sizeof(char), 1, stdout);
}

This is my putchar implementation(my_put_char.c).

#include <stdio.h>
#include <stdlib.h>
#include <stdarg.h>
#include "printf.h"

int my_printf(char *str, ...)
{   
    if(str == NULL)
        return 0;

    int i;
    char a;

    va_list print;
    va_start(print,str);

    for(i = 0; str[i] ; i++)
    {
        if(str[i] == '%')
        {
            i++;
            switch(str[i])
            {
                case 'c':
                a = va_arg(print, char);
                my_put_char(a);
                break;
            }
        }
     }
     va_end(print);
     return 0;
}

At last, this is a part of my printf implementation. I'm testing with %c to display a character.

When I do my_print("%c", 'd'); from main.c it compiles and displays d.

But when I do my_print("%c", "hi"); , it still compiles and displays a number.

Question:

After(or before) writing a = va_arg(print, char); Is there a way to check whether my input is a different data type? I'm trying to display an error if my input is a different data type.

I'm on this subject for 2 days and couldn't find any answer. Thank you so much for your time!