#include<stdio.h>
#include<windows.h>

int main()
{
    STARTUPINFO si = { sizeof(si)};
    PROCESS_INFORMATION pi = {0};

    // create the custom env
    char custom_env[] = "MY_VAR=HELLOCHILD\0\0";

    if(CreateProcess("C:\\Windows\\System32\\notepad.exe",NULL,NULL,NULL,FALSE,0,custom_env,NULL,&si,&pi))
    {
        printf("process created successfully\n");
        printf("Process ID: %lu\n",pi.dwProcessId);
        // close handle
        CloseHandle(pi.hProcess);
        CloseHandle(pi.hThread);
        getchar();
    }
    else
    {
        printf("Error: %lu\n",GetLastError());
        return 1;
    }
    return 0;
}