Thread: Ignoring specific characters in a string

Well you could consider making a copy of your string, copying only those characters you wish to check with.

Originally Posted by seanksg

My roommate just suggested that to me. It seems to make the most sense. I'm assuming I'd use something like strcpy(). But how would i keep from copying the unwanted characters?

Don't use strcpy. Instead use a loop to go over the string character by character. For each character that is a letter, copy it into the new string.

Code:

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

#define TRUE 1
#define FALSE 0

int pal(char *input);

int main( )
{
	char *stop = "done";
	char input[81];

	printf("\nEnter a string of characters for palindrome verification: ");
	scanf("%80s", input);
		
	while (strcmp(input,stop) != 0)
	{
		printf("\n%s\n\n", input);
		if (pal(input))
		{
			printf("Input is a palindrome\n\n");
		}
		else
		{
			printf("Input is not a palindrome");
		}
		printf("\n\nEnter a string of characters for palindrome verification: ");
		scanf("%80s", input);
	}

	printf("\n******Program Terminated******\n\n");
		
   	return (EXIT_SUCCESS);
}
int pal(char *input)
{
	int length = strlen(input) - 1;
	int i = 0;
	int j = length;
	char start = input[i];
	char end = input[j];
	int exit = 0;

	while (TRUE && (exit = 0))
	{
		while (isalpha(start) != 0)
		{
			++i;
		}
		while (isalpha(end) != 0)
		{
			--j;
		}
		if (i > j)
		{
			return (1);
		}
		else
		{
			while (isalpha(end) == 0 && isalpha(start) == 0)		
			{
				if (start == end)
				{
					++i;
					--j;
				}
				else
				{
					exit = 1;
				}
			}
		}
	}

	return (0);
}

This is the code I've developed. I decided to try comparing characters individually, because I couldn't figure out how to reverse the string. Nevertheless, it doesn't work. Does anyone have any insights?

Thanks.

-Sean

Code:

while head < tail 
    if !isalpha head
        head++
    else
    if !isalpha tail
        tail--
    else
    if head == tail 
        head++
        tail--
    else
        fail
success

Quzah.

Code:

while (TRUE && (exit = 0))

You are doing an assignment here, not a comparison. You need to use the == operator.