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

int
main(int argc, char *argv[])
{
    pid_t child_pid;

    switch (child_pid = fork()) {
        case -1:
            fprintf(stderr, "fork() error\n");
            exit(EXIT_FAILURE);

        case 0:     // parent
            printf("I am parent\n");
            break;

        default:    // child
            sleep(1);
            printf("I am child");
            break;
    }

    exit(EXIT_SUCCESS);
}

output:

I am parent
I am child