Exercise 1-19

Exercise 1-19  Write a function reverse(s) that reverses the character string s.  Use it to write a program that reverses its input a line at a time.

I note that there may be better ways of writing a program that reverses its input (such as a recursive function), but this program satisfies the specification exactly.

#include <stdio.h>

#define LINELENGTH 100

int reverse(char *s)

{

  char *end = s;

  while (*end)

    end++;    /* end points to the null. */

  end--;

  while (end>s)

  {

    char temp;

    temp = *end;

    *end = *s;

    *s = temp;

    end--;

    s++;

  }

}

int main(void)

{

  int c;

  int bufpos = 0;

  char buffer[LINELENGTH];

  do

  {

    c = getchar();

    switch(c)

    {

    case '\n':

      buffer[bufpos] = 0;

      reverse(buffer);

      puts(buffer);

      bufpos = 0;

      break;

    case EOF:

      buffer[bufpos] = 0;

      reverse(buffer);

      printf("%s", buffer);

      break;

    default:

      buffer[bufpos++] = c;

      if (bufpos == LINELENGTH)

      {

        printf("Buffer overflow.\n");

        return 1;

      }

      break;

    }

  }

  while(c!=EOF);

  return 0;

}