I've been getting segmentation fault and I don't know why. I have a feeling that it's caused by the code under if(isPalindrome(str_array[i]) == 0) but I don't know which one and what to do about it.
P.S. I'm still a student so I would appreciate it if the suggestions do not go far from the level of code that I have here.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int isPalindrome(char check[]);
int main() {
int array_size = 5, i;
char *str_array[array_size], *palindrome_array[array_size], str_length[100];
for(i = 0; i < array_size; i++) {
printf("Enter word #%d: ", i+1);
scanf("%[^\n]%*c", str_length); //"%[^\n]%*c : pattern matching - allows inputs to have spaces
str_array[i] = (char*) malloc(sizeof(char) * strlen(str_length));
strcpy(str_array[i],str_length);
if(strcmp(str_array[i],"exit") == 0) {
break;
}
if(isPalindrome(str_array[i]) == 0) {
palindrome_array[i] = (char*) malloc(sizeof(char) * strlen(str_length));
strcpy(palindrome_array[i], str_length);
printf("'%s' is a palindrome \n", palindrome_array[i]);
} else printf("'%s' is NOT a palindrome \n", str_array[i]);
}
//BONUS: prints all the palindrome strings inputted
printf("Your palindrome words are: \n");
for(i = 0; i < array_size; i++) {
printf("%d.)%s \n", i+1, palindrome_array[i]);
}
return 0;
}
int isPalindrome(char check[]) { // from string to individual characters
int middle = strlen(check) / 2; //gets the half of the string's length
int length = strlen(check);
for(int i = 0; i < middle; i++) {
if(check[i] != check[length - i - 1]) {
return 1;
}
}
return 0;
}
There are two main drawbacks.
To allocate a memory for a string you need to reserve space for the terminating zero character '\0' of the string.
So you need to write for example
str_array[i] = (char*) malloc(sizeof(char) * ( strlen(str_length) + 1 ) );
Also the array palindrome_array was not initialized.
char *str_array[array_size], *palindrome_array[array_size], str_length[100];
As not all tested strings are palindromes then some elements of the array still stay uninitialized for some values of the index i due to this if statement
if(isPalindrome(str_array[i]) == 0) {
palindrome_array[i] = (char*) malloc(sizeof(char) * strlen(str_length));
strcpy(palindrome_array[i], str_length);
printf("'%s' is a palindrome \n", palindrome_array[i]);
} else printf("'%s' is NOT a palindrome \n", str_array[i]);
As a result this for loop
for(i = 0; i < array_size; i++) {
printf("%d.)%s \n", i+1, palindrome_array[i]);
}
can invoke undefined behavior.
You need to declare a separate index for the array and to use it instead of the index i.
In fact the array str_array is just redundant. It is enough to use these two arrays.
char *palindrome_array[array_size], str_length[100];
The parameter of the function isPalindrome should be declared with the qualifier const
int isPalindrome( const char check[]);
because the passed string is not changed within the function. Also it is much better when the function returns a npn-zero integer when a string is a palindrome and zero otherwise.
In the call of scanf you should specify the maximum length of the input string and the conversion specifier c should be removed. For example
scanf( " %99[^\n]", str_length );
Also it is unclear why there is used the magic number 5 in your program.
I would write the program the following way
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
int isPalindrome( const char s[] )
{
size_t i = 0, n = strlen( s );
while (i < n / 2 && s[i] == s[n - i - 1]) ++i;
return i == n / 2;
}
int main( void )
{
char **p = NULL;
size_t total = 0;
size_t count = 0;
while (1)
{
char s[100];
printf( "Enter a word (to exit just press Enter): " );
if (scanf( "%99[^\n]%*c", s ) != 1 || s[0] == '\0') break;
++total;
if (isPalindrome( s ))
{
printf( "\"%s\" is a palindrome\n", s );
char **tmp = realloc( p, ( count + 1 ) * sizeof( char * ) );
if (tmp == NULL)
{
puts( "Memory allocation error. It is impossible to store the string." );
break;
}
p = tmp;
p[count] = malloc( strlen( s ) + 1 );
if (p[count] == NULL )
{
puts( "Memory allocation error. It is impossible to store the string." );
break;
}
strcpy( p[count], s );
++count;
}
else
{
printf( "\"%s\" is NOT a palindrome\n", s );
}
}
printf( "\nAmong the entered %zu words there are %zu palindrome(s).\n", total, count );
if (count != 0)
{
puts( "They are:" );
for (size_t i = 0; i < count; i++)
{
printf( "\"%s\"\n", p[i] );
}
}
for (size_t i = 0; i < count; i++)
{
free( p[i] );
}
free( p );
}
Its output might look like
Enter a word (to exit just press Enter): 1
"1" is a palindrome
Enter a word (to exit just press Enter): 12
"12" is NOT a palindrome
Enter a word (to exit just press Enter): 122
"122" is NOT a palindrome
Enter a word (to exit just press Enter): 1221
"1221" is a palindrome
Enter a word (to exit just press Enter): 12321
"12321" is a palindrome
Enter a word (to exit just press Enter):
Among the entered 5 words there are 3 palindrome(s).
They are:
"1"
"1221"
"12321"