How do you spawn another process in C?

#include <stdlib.h>

int main()
{
    system("echo HAI");

    return 0;
}

#include <stdio.h>

int main()
{
  int entry = 1;
  char line[200];
  FILE* output = popen("/usr/bin/ls -1 /usr/man", "r");
  while ( fgets(line, 199, output) )
  {
    printf("%5d: %s", entry++, line);
  }
}

1: cat1
2: cat1b
3: cat1c
4: cat1f
5: cat1m
6: cat1s
...

int system(const char *string);

QString program = "./yourspawnedprogram";
 QProcess * spawnedProcess = new QProcess(parent);
 spawnedProcess->start(program);
 // or spawnedProcess->startDetached(program);

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

int main()
{
    printf( "hi 2 un" );
    int mypid = fork();

    if( 0 == mypid )
        printf( "lol childn" );
    else
        printf( "lol parentn" );

    return( 0 );
}