Storing a string in another variable in C - c

Question

I am writing a program to check if the given string is a palindrome or not. I wrote a function to reverse the string but unable to store the reversed string in a different variable.
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
char stringPalindrome(char s[100], int i, int n){
char reversed = "";
for(i=n;i>=0;i--){
reversed += s[i];
}
return reversed;
}
int main(){
char s[100];
int i,n;
gets(s);
n = strlen(s)-1;
printf("%s", stringPalindrome(s,i,n));
return 0;
}
Is there a way to store a string in another variable without using pointers or malloc or calloc since I am new to this language and I have lots to learn

Answer 1

The goal here is not to check if a string is a palindrome but to reverse a string.
There are several problems in your code
char reversed = ""; is wrong, reversed is a char , not a char*nor aconst char *`
reversed += s[i]; does not appends s[i] as you expected
the parameter i of stringPalindrome has no sense, i must be a local variable, not a parameter
never use gets, if the input is longer than the receiving array the behavior is undefined
printf("%s", stringPalindrome(s,i,n)); as an undefined behavior because stringPalindrome returns a char rather than a string
The function stringPalindrome cannot store the reverse string in a local variable being an array of character then return that array whose has an undefined behavior. You can letting the input string unchanged :
use a static local variable in stringPalindrome, but each call of the function modifies the string made by a previous call
dynamically allocate the reverse string in the heap using malloc in stringPalindrome, in that case the caller has the responsibility to free the array when it stops to use it
also receive the array memorizing to the reversed string in parameter, as an out parameter, in hat case it is the responsibility of the caller to give an array enough long to store the result
Out of that in C the function strcat allows to concatenate strings, but in your case you want to add one char so directly assign that character rather than to use an expensive call to strcat (also supposing both strings are null terminated)
Using a global variable, the function has to take care to not write out of its static array :
#include <stdio.h>
#include <string.h>
char * stringPalindrome(const char * s, size_t n)
{
static char reversed[100];
size_t i;
if (n > sizeof(reversed) - 1)
n = sizeof(reversed) - 1;
for (i = 0; i < n; ++i)
reversed[i] = s[n - i - 1];
reversed[i] = 0;
return reversed;
}
int main()
{
char s[100];
if (fgets(s, sizeof(s), stdin) != NULL)
puts(stringPalindrome(s, strlen(s) - 1));
return 0;
}
Compilation and execution :
pi#raspberrypi:/tmp $ ./a.out
azer ty
yt reza
pi#raspberrypi:/tmp $
Using dynamic allocation :
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
char * stringPalindrome(const char * s, size_t n)
{
char * reversed = malloc(n + 1);
size_t i;
for (i = 0; i < n; ++i)
reversed[i] = s[n - i - 1];
reversed[i] = 0;
return reversed;
}
int main()
{
char s[100];
if (fgets(s, sizeof(s), stdin) != NULL) {
char * r = stringPalindrome(s, strlen(s) - 1);
puts(r);
free(r);
}
return 0;
}
Compilation and execution :
pi#raspberrypi:/tmp $ ./a.out
azer ty
yt reza
pi#raspberrypi:/tmp $
Managing the result in an output parameter :
#include <stdio.h>
#include <string.h>
char * stringPalindrome(const char * s, char * reversed, size_t n)
{
size_t i;
for (i = 0; i < n; ++i)
reversed[i] = s[n - i - 1];
reversed[i] = 0;
return reversed;
}
int main()
{
char s[100];
char r[100];
if (fgets(s, sizeof(s), stdin) != NULL) {
puts(stringPalindrome(s, r, strlen(s) - 1));
puts(r);
}
return 0;
}
Compilation and execution :
pi#raspberrypi:/tmp $ gcc -Wall s.c
pi#raspberrypi:/tmp $ ./a.out
azer ty
yt reza
yt reza
pi#raspberrypi:/tmp $

Answer 2

Well, no.
There is no string type in C. All we have are pointers to chars. And by convention the string runs from the given location up to the fist zero byte that follows. There is no way to escape that.
But in order to find out whether a string is a palindrome or not, you do not have to reverse if first. Just compare the first with the last character if they match continue with the second and second to last and so on. Until a pair does not match. If you run out of pairs to compare (when they meet in the middle) the string is a palindrome. That way you can sidestep the issue of creating a new string.

Answer 3

The simplest way to do this is to loop over the string and compare start and end characters. Use fgets() which allows you to set the max length of the string, gets() has no check so it should be avoided.
int palindrom()
{
char s[100];
if (fgets(s,sizeof s,stdin) != NULL)
{
int len = strlen(s);
if (s[len-1] == '\n') --len; // if string is 100 chars there is no \n
for (char* p = s, *q = s + len - 1; p >= q; ++p,--q)
{
if (*p != *q) return 0; // look until difference
}
return 1; // palindrome
}
puts("no input");
return 0;
}

Answer 4

first of all great that you started with programming.
There are three little points in your code:
You are using gets() which is a dangerous for buffer overflow, so I used fgets() here. Does not matter if you do not know what that means, because that is something advanced, but if you want to know more about that, let me know.
In printf() you want to print a string (%s) but your function stringPalindrome does return a char instead of an array of chars. Therefore you obtained an error. I fixed this by declaring the function to be of type const char*. Also char reversed = ""; defines an empty character, so in the for loop you are trying to append characters to an empty character and this gives you a memory error. I fixed this by using a second array of characters (r) like s and added him to the parameters of the function call.
Finally the for loop itself. This problem raised out of the second pa
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
const char* stringPalindrome(char s[100], char r[100], int i, int p, int n){
for(i=0;i<p;i++){
r[i] = s[n];
n--;
}
return r;
}
int main(){
char s[100];
char r[100];
int i,n,p;
fgets(s, 100, stdin);
p = strlen(s);
n = p-1;
printf("%s", stringPalindrome(s,r,i,p,n));
return 0;
}