如何在C中打印没有库函数的变量的charcater,字符串或值？

#include<stdio.h>

void print_char(char c) {
    putchar(c);
}

void print_string(char *str) {
    for (int i = 0; str[i] != '\0'; i++) {
        putchar(str[i]);
    }
}

void print_int(int num) {
    if (num < 0) {
        putchar('-');
        num = -num;
    }
    if (num >= 10) {
        print_int(num / 10);
    }
    putchar(num % 10 + '0');
}

int main() {
    char c = 'A';
    char str[] = "Hello, world!";
    int num = 12345;

    print_char(c);
    putchar('\n');
    print_string(str);
    putchar('\n');
    print_int(num);
    putchar('\n');

    return 0;
}