Thread: Comparing string arrays

I'm trying to get my program to store only letters in two arrays. So far I have:

Code:

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

main () {

   printf("Enter something: ");
   char temp[100];

   fgets(temp, 100, stdin);

   int c;
   int letters = 0;
   for (c = 0; c <= strlen(temp); c++) {
      if (isalpha(temp[c])) {
         letters++;
           }
         }

   int *ptr;
   ptr = &letters;
   char str[*ptr];
   char rev[*ptr];
   printf("Letters amount: %d\n", *ptr);

   int i;
   int k = 0;
   for (i = 0; i < strlen(temp); i++) {
   if (isalpha(temp[i])) {
         str[k] = temp[i];
         k++;
           }
        }

   k = 0;
   for(i = strlen(str)-1; i >= 0; i--){

        rev[k] = str[i];
      k++;
    }



   printf("You entered: %s\n", str);
   printf("The reverse: %s\n", rev);

}

If I put "Test":
You entered: Test
The reverse: tseT

If I put "Testing One Two Three":
You entered: TestingOneTwoThree
The reverse: eerhTowTenOgnitseT@

If I put "Testinggg":
You entered: Testingggggaj<@
The reverse: @<jagggggnitseT

I have to get str[] and rev[] to store only letters because I will have to compare them later.

I understand that it has something to do with the null-byte terminator in arrays, so how can I adjust my code so that it stores the letters correctly?

I'll post an example in an edit to this post.

Code:

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

#define SIZE 100

int main() {
  int i, n;
  char s[SIZE]="";
  char ch;
  printf("\n\nEnter some letters and numbers, and etc. Only letters will go into the array s[]\n");
  i=0;
  while((ch=getc(stdin)) != EOF) { //EOF is Ctrl+Z
    if(isalpha(ch)) {
      s[i++]=ch;
    }
  }

  printf("\n%s", s);

  printf("\n\n\t\t\t     press enter when ready");
  (void) getchar(); 
  return 0;
}

variable++ increments the variable by one.

Yes, you should use a char array.

Originally Posted by Adak

I'll post an example in an edit to this post.

Code:

  char ch;
  printf("\n\nEnter some letters and numbers, and etc. Only letters will go into the array s[]\n");
  i=0;
  while((ch=getc(stdin)) != EOF) { //EOF is Ctrl+Z

The value EOF cannot be stored in a char. It is a negative integer type, that holds no char representable value.


Quzah.

Hit Ctrl+z, then the Enter key to quit.

@Quzah:

Why can't an unsigned char be negative? My unsigned chars (the default), have a range from -128 to 127.

Originally Posted by Adak

@Quzah:

Why can't an unsigned char be negative?

What? Why can't unsigned be negative? Did you really just type that?

Originally Posted by Adak

My unsigned chars (the default), have a range from -128 to 127.

It doesn't matter. EOF is guaranteed to not be a negative value that is representable in a char. It's not guaranteed to be -1. There's a reason all those scores of standard functions return ints instead of chars.


Quzah.

OK, thanks Quzah.

So Never_lose, if you can't get it to work, your EOF is unrepresentable as a char. I'll post up a new version, with int's instead.

The netbeans system has a different EOF value. Most systems used -1, years ago, but now the standards committee for C decided to change EOF to be a non-char value.

It works fine for me, but let's make it something standard.

Code:

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

#define SIZE 100

int main() {
  int i, n;
  char s[SIZE]="";
  
  printf("\n\nEnter some letters and numbers. Only letters will go into s[]\n");
  i=0;
  while ((n = getchar()) != '\n') {
    if(isalpha(n)) 
      s[i++] = n;
  }

  printf("\n%s", s);

  printf("\n\n\t\t\t     press enter when ready");
  (void) getchar(); 
  return 0;
}

Ok, thanks... and what is the purpose of (void) getchar();?

Never mind, it must be so that the user can "press enter when ready."

I've finally finished my program by the way, thanks for the help!

Originally Posted by Adak

Most systems used -1, years ago, but now the standards committee for C decided to change EOF to be a non-char value.

No, it's always been that way. They didn't just change it.

The problem is that if you are say reading a binary file one byte at a time, and you are taking those bytes and sticking them in a char, and you are testing that against EOF, then some random byte in your file will trigger EOF in your comparison. You'll think you've hit the end of your file when you haven't.


Quzah.

Question 12.1b
if you have read K&R since that time eof is negative value.
Because it works with my turbo c for tenty years does not make it correct.