#include <stdio.h>
   #include <ctype.h>

   main() /* lower: convert input to lower case*/
   {
       int c

       while ((c = getchar()) != EOF)
           putchar(tolower(c));
       return 0;
   }

   #include <stdarg.h>

   /* minprintf: minimal printf with variable argument list */
   void minprintf(char *fmt, ...)
   {
       va_list ap; /* points to each unnamed arg in turn */
       char *p, *sval;
       int ival;
       double dval;

       va_start(ap, fmt); /* make ap point to 1st unnamed arg */
       for (p = fmt; *p; p++) {
           if (*p != '%') {
               putchar(*p);
               continue;
           }
           switch (*++p) {
           case 'd':
               ival = va_arg(ap, int);
               printf("%d", ival);
               break;
           case 'f':
               dval = va_arg(ap, double);
               printf("%f", dval);
               break;
           case 's':
               for (sval = va_arg(ap, char *); *sval; sval++)
                   putchar(*sval);
               break;
           default:
               putchar(*p);
               break;
           }
       }
       va_end(ap); /* clean up when done */
   }

   #include <stdio.h>

   main()  /* rudimentary calculator */
   {
       double sum, v;

       sum = 0;
       while (scanf("%lf", &v) == 1)
           printf("\t%.2f\n", sum += v);
       return 0;
   }

   while (getline(line, sizeof(line)) > 0) {
       if (sscanf(line, "%d %s %d", &day, monthname, &year) == 3)
           printf("valid: %s\n", line); /* 25 Dec 1988 form */
       else if (sscanf(line, "%d/%d/%d", &month, &day, &year) == 3)
           printf("valid: %s\n", line); /* mm/dd/yy form */
       else
           printf("invalid: %s\n", line); /* invalid form */
   }

   #include <stdio.h>

   /* cat:  concatenate files, version 1 */
   main(int argc, char *argv[])
   {
       FILE *fp;
       void filecopy(FILE *, FILE *)

       if (argc == 1) /* no args; copy standard input */
           filecopy(stdin, stdout);
       else
          while(--argc > 0)
              if ((fp = fopen(*++argv, "r")) == NULL) {
                  printf("cat: can't open %s\n, *argv);
                  return 1;
              } else {
                 filecopy(fp, stdout);
                 fclose(fp);
              }
          return 0;
   }

    /* filecopy:  copy file ifp to file ofp */
    void filecopy(FILE *ifp, FILE *ofp)
    {
        int c;

        while ((c = getc(ifp)) != EOF)
            putc(c, ofp);
    }

   #include <stdio.h>

   /* cat:  concatenate files, version 2 */
   main(int argc, char *argv[])
   {
       FILE *fp;
       void filecopy(FILE *, FILE *);
       char *prog = argv[0];  /* program name for errors */

       if (argc == 1 ) /* no args; copy standard input */
           filecopy(stdin, stdout);
       else
           while (--argc > 0)
               if ((fp = fopen(*++argv, "r")) == NULL) {
                   fprintf(stderr, "%s: can't open %s\n",
                           prog, *argv);
                   exit(1);
               } else {
                   filecopy(fp, stdout);
                   fclose(fp);
               }
       if (ferror(stdout)) {
           fprintf(stderr, "%s: error writing stdout\n", prog);
           exit(2);
       }
       exit(0);
   }

   /* fgets:  get at most n chars from iop */
   char *fgets(char *s, int n, FILE *iop)
   {
       register int c;
       register char *cs;

       cs = s;
       while (--n > 0 && (c = getc(iop)) != EOF)
           if ((*cs++ = c) == '\n')
               break;
       *cs = '\0';
       return (c == EOF && cs == s) ? NULL : s;
   }

   /* fputs:  put string s on file iop */
   int fputs(char *s, FILE *iop)
   {
       int c;

       while (c = *s++)
           putc(c, iop);
       return ferror(iop) ? EOF : 0;
   }

   /* getline:  read a line, return length */
   int getline(char *line, int max)
   {
       if (fgets(line, max, stdin) == NULL)
           return 0;
       else
           return strlen(line);
   }