int MPI_Comm_rank(MPI_Comm communicator,
                  int rank);

#include <stdio.h>
#include <stdlib.h>
#include <mpi.h>

/**
 * @brief For each process in the default communicator MPI_COMM_WORLD, show their rank.
 **/
int main(int argc, char* argv[])
{
    MPI_Init(&argc, &argv);

    int my_rank;
    MPI_Comm_rank(MPI_COMM_WORLD, &my_rank);

    printf("I am MPI process %d.\n", my_rank);

    MPI_Finalize();

    return EXIT_SUCCESS;
}

SUBROUTINE MPI_Comm_rank(communicator, rank, ierror)
    INTEGER :: communicator
    INTEGER :: rank
    INTEGER :: ierror

!> @brief For each process in the default communicator MPI_COMM_WORLD, show their rank.
PROGRAM main
    USE mpi

    IMPLICIT NONE

    INTEGER :: ierror
    INTEGER :: my_rank

    CALL MPI_Init(ierror)

    CALL MPI_Comm_rank(MPI_COMM_WORLD, my_rank, ierror)

    WRITE(*,'(A,I0,A)') 'I am MPI process ', my_rank, '.'

    CALL MPI_Finalize(ierror)
END PROGRAM main

SUBROUTINE MPI_Comm_rank(communicator, rank, ierror)
    TYPE(MPI_Comm), INTENT(IN) :: communicator
    INTEGER, INTENT(OUT) :: rank
    INTEGER, OPTIONAL, INTENT(OUT) :: ierror

!> @brief For each process in the default communicator MPI_COMM_WORLD, show their rank.
PROGRAM main
    USE mpi_f08

    IMPLICIT NONE

    INTEGER :: my_rank

    CALL MPI_Init()

    CALL MPI_Comm_rank(MPI_COMM_WORLD, my_rank)

    WRITE(*,'(A,I0,A)') 'I am MPI process ', my_rank, '.'

    CALL MPI_Finalize()
END PROGRAM main