#include <stdio.h>

int main(void)
{
  char c = 'A';
  char s[] = "Blue moon!";

  printf("[%c]\n[%2c]\n[%-3c]\n[%s]\n[%3s]\n[%.6s]\n[%-11.8s]\n",
    c, c, c, s, s, s, s);
  return 0;
}

#include <stdio.h>

int main(void)
{
  int i = 123;
  double x = 0.123456789;

  printf("[%d]\n[%05d]\n[%7o]\n[%-9x]\n[%-#9x]\n[%10.5f]\n[%-12.5e]\n",
  i, i, i, i, i, x, x);
  return 0;
}

#include <assert.h>
#include <stdio.h>
#include <string.h>

#define MAXSTRING 100

int main(void)
{
  char input[MAXSTRING];
  char string[15];
  char *val;
  char c;
  int cnt;
  int i;
  int n;
  FILE *ifp;

  ifp = fopen("input", "r");
  assert(ifp != NULL);
  val = fgets(input, MAXSTRING, ifp);
  assert(val != NULL);
  fclose(ifp);
/*
// Delete the newline at the end of the input string.
*/
  n = strlen(input);
  *(input + n - 1) = '\0';
  cnt = sscanf(input, "%d , %*s %% %c %5s %s", &i, &c, string,   &string[5]);
  printf("%s%s%s%c%s%d%s%s%s%s%s%d%s\n",
    "---\n"
    "Control string: \"%d , %*s %% %c %5s %s\"\n" 
    "\n"
    " Input string: \"", input, "\"\n"
    "\n"
    "Here are the values obtained from the input string:\n"
    "\n"
    " c = ", c, "\n"
    " i = ", i, "\n"
    " string = ", string, "\n"
    " string + 5 = ", string + 5, "\n"
    "\n"
    " number of successful conversions = ", cnt, "\n");
  return 0;
}

45 , ignore_this % C read_in_this**

#include <stdio.h>
#include <stdlib.h>

void double_space(FILE *, FILE *);
void prn_info(char *);

int main(int argc, char **argv)
{
  FILE *ifp, *ofp;

  if (argc != 3) {
    prn_info(argv[0]);
    exit(1);
  }
  ifp = fopen(argv[1], "r"); /* open for reading */
  ofp = fopen(argv[2], "w"); /* open for writing */
  double_space(ifp, ofp);
  fclose(ifp);
  fclose(ofp);
  return 0;
}

void double_space(FILE *ifp, FILE *ofp)
{
  int c;

  while ((c = getc(ifp)) != EOF) {
    putc(c, ofp);
    if (c == '\n')
      putc('\n', ofp); /* found a newline - duplicate it */
  }
}

void prn_info(char *pgm_name)
{
  printf("\n%s%s%s\n\n%s%s\n\n",
    "Usage: ", pgm_name, " infile outfile",
    "The contents of infile will be double-spaced ",
    "and written to outfile.");
}

/* Write a file backwards. */

#include <stdio.h>

#define MAXSTRING 100

int main(void)
{
  char fname[MAXSTRING];
  int c;
  FILE *ifp;

  fprintf(stderr, "\nInput a filename: ");
  scanf("%s", fname);
  ifp = fopen(fname, "rb"); /* binary mode for MS_DOS */
  fseek(ifp, 0, SEEK_END); /* move to end of the file */
  fseek(ifp, -1, SEEK_CUR); /* back up one character */
  while (ftell(ifp) > 0) {
    c = getc(ifp); /* move ahead one character */
    putchar(c);
    fseek(ifp, -2, SEEK_CUR); /* back up two characters */
  }
  return 0;
}

/* Change the case of letters in a file. */

#include <ctype.h>
#include <fcntl.h>
#include <unistd.h> /* use io.h in MS_DOS */

#define BUFSIZE 1024

int main(int argc, char **argv)
{
  char mybuf[BUFSIZE], *p;
  int in_fd, out_fd, n;

  in_fd = open(argv[1], O_RDONLY);
  out_fd = open(argv[2], O_WRONLY | O_EXCL | O_CREAT, 0600);
  while ((n = read(in_fd, mybuf, BUFSIZE)) > 0) {
    for (p = mybuf; p - mybuf < n; ++p)
      if (islower(*p))
        *p = toupper(*p);
      else if (isupper(*p))
        *p = tolower(*p);
      write(out_fd, mybuf, n);
  }
  close(in_fd);
  close(out_fd);
  return 0;
}