Creating a process

#include <sys/types.h>
#include <unistd.h>
#include <iostream>
#include <cerrno>
#include <sys/wait.h>
 
int main(){
 
    // starting a parent process
    std::cout << "Parent process started... " << std::endl;
 
    // create a child process by cloning the current one 
    pid_t child = fork();
 
    // make sure we did not fail while creating a process
    if(child == -1){
        return errno;
    }
 
    // if the return value of the fork() is 0, then we are now running in the child process
    // if the return value of the fork() is positive, then we are running inside the parent process
    if(child == 0){
        // this will be printed ONLY from the child process
        std::cout << "Child process says hello. PID: " << getpid() << std::endl;
    }
    else if(child > 0){
        // this will be printed ONLY from the parent process
        std::cout << "This will only be executed in the parent process. PID: " << getpid() << std::endl;
    }
 
    // this message will be printed twice: from both parent and child processes
    std::cout << "General hello from " << getpid() << std::endl;
 
    // wait for the child only in the parent
    if(child > 0){
        
        // a variable to keep the exit code of the child process once it finishes
        int childStatus = -1;
 
        // wait for the completion of the child process
        pid_t waitingChildPid = waitpid(child, &childStatus, 0);
 
        // child process completes its execution with a "childStatus" exit code
        std::cout << "Child process is over, we can complete parent as well. Child process exit code " << childStatus << std::endl;
    }
 
    // process completion message from both processes
    std::cout << "Completing process " << getpid() << std::endl;
 
    return 0;
}

g++ fork.cpp -o fork
./fork

Parent process started...
This will only be executed in parent process. PID: 328
General hello from 328
Child process says hello. PID: 329
General hello from 329
Completing process 329
Child process is over, we can complete parent as well. Child process exit code 0
Completing process 328