Taking input and Outputting it backwards

I'm not sure what the problem is here, but I can get the program to produce, "Hello" as "olleH" but when I type something like,
"Hello my nick is whtpirate" I only get "olleH" what seems to be the problem ? I would appreciate help thank you :)

Code:

---

#include <stdio.h>

// Take user input and Output it backwards.

int a;
char choice[200];

int main()
{
 // Gotta put my little plug in there as usual :)
 printf("\n Text reverser; Coded by whtpirate(elder(justin)) of LogiTeam.\n");
 puts("\n");
  // Begin Main;
  printf("\tPlease enter a string: ");
  scanf("%199s", choice);
  for (a = strlen(choice) + 1; a != -1; a--) // This should make the text go backwards.
  {
    printf("%c", choice[a]);
  }
 return 0;
}

---

The %s format specifier to scanf is whitespace delimited. Have you looked at the FAQ?

thanks for the help, works perfectly now :)

Code:

---

#include <stdio.h>

// Take user input and Output it backwards.

int a;
char choice[200];

int main()
{
 // Gotta put my little plug in there as usual :)
 printf("\n Text reverser; Coded by whtpirate(elder(justin)) of LogiTeam.\n");
 puts("\n");
  // Begin Main;
  printf("\tPlease enter a string: ");
  fgets(choice, 200, stdin);
  for (a = strlen(choice) + 1; a != -1; a--) // This should make the text go backwards.
  {
    printf("%c", choice[a]);
  }
 return 0;
}

---

Actually, your loop has a bug. You assign a with a value that could be outside the bounds of the array. Other thoughts:

Code:

---

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

int main(void)
{
  char buffer[BUFSIZ];
  /*
    * Prompt the user. Ensure that the prompt is displayed.
    */
  fputs("Please enter a string: ", stdout);
  fflush(stdout); /* http://www.eskimo.com/~scs/C-faq/q12.4.html */
  /*
    * Get one line of input.
    * Checking return values is a good habit to have.
    */
  if ( fgets(buffer, sizeof(buffer), stdin) != NULL )
  {
      size_t i; /* strlen() returns a size_t */
      /*
      * Look for a newline ('\n') in the input string.
      * If found, replace it with a terminating null character ('\0').
      */
      char *ch = strchr(buffer, '\n');
      if ( ch != NULL )
      {
        *ch = '\0';
      }
      /*
      * Set the index to the end of the string.
      *
      * If we had a 3-character string "abc", strlen() would return 3.
      * This would mean that buffer[0] == 'a', buffer[1] == 'b',
      * buffer[2] == 'c', and buffer[3] == '\0' (the null termination).
      *
      * So we subtract 1 from strlen(buffer) so that buffer[i] is the
      * last character immediately preceding the null termination.
      */
      i = strlen(buffer) - 1;
      do
      {
        putchar(buffer[i]);
      } while ( i-- > 0 ); /* we want to print until buffer[0] and then stop */
      /*
      * It is a good idea to make sure programs that output to the stdout
      * finish with a newline.
      */
      putchar('\n');
  }
  return 0;
}

/* my output
Please enter a string: Hello my nick is whtpirate
etaripthw si kcin ym olleH
*/

---

Code:

---

#include <stdio.h>
void p( void )
{
    int c = fgetc( stdin );
    if( c == '\n' )
        return;
    p( );
    fputc( c, stdout );
}
int main ( void )
{
    printf("Enter a string:\n");
    p();
    return 0;
}

---

I'm partial to this method myself.

Quzah.

Cute quzah!! ;)

Actually, Dave, your loop has a problem too. And a suggestion.

1) the suggestion:

Quote:

---

/*
* Look for a newline ('\n') in the input string.
* If found, replace it with a terminating null character ('\0').
*/
char *ch = strchr(buffer, '\n');
. . .
i = strlen(buffer) - 1;

---

Why use the overhead of strchr()? Move the strlen() above and the '\n', if it exists, will be at buffer[i]. Just check it directly.

2) the problem:

Quote:

---

* So we subtract 1 from strlen(buffer) so that buffer[i] is the
* last character immediately preceding the null termination.
*/
i = strlen(buffer) - 1;
do
{
putchar(buffer[i]);
} while ( i-- > 0 );

---

If just RETURN was pressed, this will process buffer[-1], which is not a good thing. In this case a while loop would be safer.

Code:

---

i = strlen(buffer) - 1;    /* get end of string */
while (i >= 0)            /* while there's still string left */
{
    putchar(buffer[i--]);  /* output char, dec i */
}
=== or ===
i = strlen(buffer);        /* get str length */
while (i)                  /* while not a start of string */
{
    putchar(buffer[--i]);  /* dec i and display the character */
}

---

Very good code quzah!!

Code:

---


void p( void )
{
    int c = fgetc( stdin );
    if( c == '\n' )
        return;
    p( );        // where do we go from here?
    fputc( c, stdout );
}

// maybe

char * strtail(const char * data)
{
 char * ptr  = (char*)data;
 while(*ptr) ptr++;
 return ptr;
}


char * strev(char * buffer, const char * data)
{
 char * end = strtail(data), * ptr = buffer;
 while(end != data)  *(ptr++) = *(--end);
 *ptr = 0;
 return buffer;
}

char * strevget(char * buffer, int length)
{
 return strev(fgets(buffer, length, stdin));
}

---

Quote:

---

Originally posted by WaltP
Actually, Dave, your loop has a problem too. And a suggestion.

1) the suggestion:Why use the overhead of strchr()? Move the strlen() above and the '\n', if it exists, will be at buffer[i]. Just check it directly.

---

That works for me. I was just putting some of the suggested FAQ code into the example.

Quote:

---

Originally posted by WaltP
2) the problem: If just RETURN was pressed, this will process buffer[-1], which is not a good thing. In this case a while loop would be safer.

---

D'oh! I hate it when I miss stuff like that.

Quote:

---

Originally posted by WaltP

Code:

---

i = strlen(buffer) - 1;    /* get end of string */
while (i >= 0)            /* while there's still string left */
{
    putchar(buffer[i--]);  /* output char, dec i */
}

---

---

When is a size_t not greater than or equal to 0? I think prefer the second option.

Code:

---

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

int main(void)
{
  char buffer[BUFSIZ];
  fputs("Please enter a string: ", stdout);
  fflush(stdout);
  if ( fgets(buffer, sizeof(buffer), stdin) != NULL )
  {
      size_t i = strlen(buffer);
      if ( i > 0 )
      {
        if ( buffer[i - 1] == '\n' )
        {
            --i;
        }
        while ( i-- > 0 )
        {
            putchar(buffer[i]);
        }
        putchar('\n');
      }
  }
  return 0;
}

---

I did not get a chance to read through all of the postings,
I am running out.

However I did see one immediate problems with your code,
which is:

1. No inclusion of <string.h> for the usage of the
strlen() function
#include <string.h>

Added Suggestions

Wen using the puts() function, it is not necessary
to add the newline escape sequence \n within the
puts() function ... unless your intent was to
have two newline characters. You could simply
use puts("");

I see that you want to ALWAYS pump your credits in your
output of your code ... that's perfectly normal ...
however, you might want to create a function such as

void whtpirate(); /* whtpirate function prototyp */
void whtpirate()
{
printf("\n Text reverser; Coded by whtpirate(elder(justin)) of LogiTeam.\n");
};

If you create the function out of the main() function
you could call the whtpirate() from any other funtion
that you might create.

I hope that my suggestions and correction help you.

I wish you the best in your coding.