Thread: Palindromes - Determining the _Bool function

Hey guys!

I am working on a palindrome assignment and I have pretty much everything figured out up until the end. Here is my code so far:

Code:

#include <stdio.h>#define TRUE 1
#define FALSE 0


void make_copy_of_string(char str[], char str_copy[]);
void keep_chars(char string[]);
void convert_uper_to_lower_case(char string[]);
_Bool palindromness(char string[]);


int main(void)
{


    char phrase[101]; //create array to hold input
    char phrase_copy[101]; //array that holds copy of input which will be modified


    printf("Enter a phrase: ");
    fgets(phrase, 101, stdin); //stores input into 'phrase' with a max 100 chars
    printf("%s\n", phrase); //tests if fgets is working


    make_copy_of_string(phrase, phrase_copy); //makes a copy of phrase
    printf("%s\n\n", phrase_copy);


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


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




    return 0;
}


void make_copy_of_string(char str[], char str_copy[])
{
    int i = 0; //to keep track of which char is being copied


    while(str[i] != '\n' && str[i] != '\0')
    {
        str_copy[i] = str[i];
        i++;
    }
    str_copy[i] = '\0';
    str[i] = '\0';
}


void keep_chars(char string[])
{
    int i=0, j=0;


    while (string[i] != '\0')
    {
        if ( ('A'<= string[i] && string[i] <= 'Z') || ('a' <= string[i] && string[i] <= 'z'))
        {
            string[j] = string[i];
            i++;
            j++;
        }
        else
            i++;
    }
    string [j] = '\0';
}


void convert_uper_to_lower_case(char string[])
{
    int i = 0;


    while (string[i] != '\0')
    {
        if ('A' <= string[i] && string[i] <= 'Z')
        {
            string[i] += 32;
            i++;
        }
        else
            i++;
    }


}


_Bool palindromeness(char string[])
{


}

The only issue I am running in, is figuring out how to set up the _Bool palindromeness function. I was thinking of perhaps making a copy of "convert_uper_to_lower_case" and doing an if loop to see if the first char matched the last char of the copy.

With this setup I described, I am still not sure how to set it up really, and I would rather work on a better method. I am only allowed to use stdio.h as well.

Originally Posted by GReaper

You need to find the length of the string( without the '\0' character of course ). Loop from 0 to length/2 and check if str[i] and str[length-i-1] are equal.

How would I check if str[i] and str[length-i-1] are the same? Also what is str[length-i-1]? I just learned about Arrays and don't know too much about them.

Originally Posted by GReaper

By using the equality operator, '=='.


Hopefully you've learned that you can address a specific element of an array by using an index, like "array[i]".
In my example, 'length' is supposed to be the string length. When you have a counter from 0 to length/2, "length-i-1" is essentially the mirror index of "i", allowing you to check if those two char are the same, and in the end if the string is a palindrome. For example:

Code:

length = 7
"i" "length-i-1"
 0       6
 1       5
 2       4
 3       3
 4       2
 5       1
 6       0

Okay that makes sense now. For some reason, I imagined you can only put 'i' into the brackets of an array for some reason. Knowing I can put an expression in the brackets opened up my mind. Here is what I got for the _Bool function:

Code:

_Bool palindromeness(char string[])
{
    int i, index_last_char;


    for(i=0; string[i] != '\0'; i++);
    index_last_char = i-1;


    for (i=0; i<=(index_last_char)/2; i++)
    {
        if(string[i] != string[index_last_char - i])
            return FALSE;
    }
    return TRUE;




}