how is printf implemented in c code example

Example 1: How to make a printf in c

#include <stdio.h>

int printf(const char *format, ...);

int main(void)
{
  int nb = 20;
 
  printf("Hello World !\n");
  printf("%d\n", nb);
  printf("%s/%d\n", "Nice", 20);
  return (0);
}

/// output :
///
///	Hello World !
///	20
///	Nice/20
///

Example 2: printf in c

/* printf example */
#include <stdio.h>

int main()
{
   printf ("Characters: %c %c \n", 'a', 65);
   printf ("Decimals: %d %ld\n", 1977, 650000L);
   printf ("Preceding with blanks: %10d \n", 1977);
   printf ("Preceding with zeros: %010d \n", 1977);
   printf ("Some different radices: %d %x %o %#x %#o \n", 100, 100, 100, 100, 100);
   printf ("floats: %4.2f %+.0e %E \n", 3.1416, 3.1416, 3.1416);
   printf ("Width trick: %*d \n", 5, 10);
   printf ("%s \n", "A string");
   return 0;
}