palindrome c program is not working for some reason - c

Question

this program checks weather the entered string is palindrome or not . it should be in a way like it should even tell the string is palindrome if there is space or any special character
like messi is a palindrome of iss em
and ronald!o is a palindrome of odlanor
this is the program and for some odd reason it is strucking and not working
#include <stdio.h>
#include <string.h>
int main() {
char palstr[100], ans[100];
printf("enter the string for checking weather the string is a palindrome or not");
scanf("%[^/n]", &palstr);
int ispalin = 1, i = 0, n = 0;
int num = strlen(palstr);
printf("the total length of the string is %d", num);
while (i <= num) {
if (palstr[i] == ' ' || palstr[i] == ',' || palstr[i] == '.' ||
palstr[i] == '!' || palstr[i] == '?') {
i++;
}
palstr[n++] == palstr[i++];
}
int j = num;
i = 0;
while (i <= num) {
ans[j--] = palstr[i];
}
printf("the reverse of the string %s is %s", palstr, ans);
if (ans == palstr)
printf("the string is a palindrome");
else
printf("the string is not a palindrome");
return 0;
}

Answer 1

A few points to consider. First, regarding the code:
if (ans == palstr)
This is not how you compare strings in C, it compares the addresses of the strings, which are always different in this case.
The correct way to compare strings is:
if (strcmp(ans, palstr) == 0)
Second, you should work out the length of the string after you have removed all unwanted characters since that's the length you'll be working with. By that I mean something like:
char *src = palstr, dst = palstr;
while (*src != '\0') {
if (*c != ' ' && *src != ',' && *src != '.' && *src != '!' && *src != '?') {
*dst++ = *src;
}
src++;
}
Third, you have a bug in your while loop anyway in that, if you get two consecutive bad characters, you will only remove the first (since your if does that then blindly copies the next character regardless).
Fourth, you may want to consider just stripping out all non-alpha characters rather than that small selection:
#include <ctype.h>
if (! isalpha(*src) {
*dst++ = *src;
}
Fifth and finally, you don't really need to create a new string to check for a palindrome (though you may still need to if you want to print the string in reverse), you can just start at both ends and move inward, something like:
char *left = &palstr, right = palstr + strlen(palstr) - 1, ispalin = 1;
while (left < right) {
if (*left++ != *right--) {
ispalin = 0;
break;
}
}
There may be other things I've missed but that should be enough to start on.

Answer 2

well, the are so many bugs in this code. I will point them out with comments.
#include <stdio.h>
#include <string.h>
int main() {
char palstr[100], ans[100];
printf("enter the string for checking weather the string is a palindrome or not\n");
scanf("%s", palstr); // your former code won't stop input util Ctrl+D
int ispalin = 1, i = 0, n = 0;
int num = strlen(palstr);
printf("the total length of the string is %d\n", num);
while (i < num) { // < insted of <=
if (palstr[i] == ' ' || palstr[i] == ',' || palstr[i] == '.' ||
palstr[i] == '!' || palstr[i] == '?') {
i++;
continue;// without this, marks still in the string
}
palstr[n++] = palstr[i++]; //should be =
}
palstr[n] = '\0'; //
num = n; // the length might be changed
i = 0;
int j = num-1; // reverse
while (i < num) { //
ans[i++] = palstr[j--]; //
}
ans[i] = '\0'; //
printf("the reverse of the string %s is %s\n", palstr, ans);
//if (ans == palstr) they can never be equal
if (strcmp(ans, palstr)==0)
printf("the string is a palindrome\n");
else
printf("the string is not a palindrome\n");
return 0;
}