/* -*- c -*- */

/* smallest */
/* the smallest running program doing nothing */
main() { return 0; }

/* hello world */
/* print a simple string on stdout */
#include <stdio.h>
main() {
    puts("Hello World");
    return 0;
}


/* argv */
/* access command line parameters (no segmentation fault accepted, nor silent exception, so some languages must explicitly check the presence of the argument) */
#include <stdio.h>
main(int n, char **argv) {
    if (n > 1) puts(argv[1]);
    return 0;
}


/* env */
/* access environment variable */
#include <stdlib.h>
main() {
    char *s = getenv("HOME");
    if (s) puts(s);
    return 0;
}


/* test file exists */
/* return exit code error (non zero) if a file does not exist */
#include <unistd.h>
main() {
    return access("/etc/mtab", F_OK);
}


/* test file readable */
/* return exit code error (non zero) if a file is not readable */
#include <unistd.h>
main() {
    return access("/etc/mtab", R_OK);
}


/* formatting */
/* print integers in a simple formatted string */
#include <stdio.h>
main() {
    int a=1, b=2;
    printf("%d + %d = %d\n", a, b, a + b);
    return 0;
}


/* system */
/* call an external program and check the return value */
#include <stdio.h>
main() {
    if (system("false")) fprintf(stderr, "false failed\n");
    system("echo done");
    return 0;
}


/* sed in place */
/* remove #-comments from a file (modifying the file, i.e. in place) */
#include <stdio.h>
#include <unistd.h>
main (int argc, char **argv)
{
 FILE *f;
 int c=1, t=0, i=0;
 if (argc-c)
  {
   f=fopen(argv[c],"r+");
   while (c) switch (c=getc(f))
    {
    case '#' : if (!t) { t=1,i-=2; break; }
    case '\n' : if (t) { t=0; break; }
    default : if (t==1) { i--; break; }
         fseek(f,i-1,1);
         putc(c++,f);
         fseek(f,-i,1);
    }
   truncate(argv[1],ftell(f)+i);
  }
 return 0;
}