Why am I getting a 'Segmentation Fault' error in my code?

Question

I have this code to check for a palindrome in C:

#include <stdio.h>

int main(void) {
    char* test="racecar";
    Palindrome(test, 7);
}

int Palindrome(char mystr[], int len){
    if(len<2)
        printf("Palindrome");
    else if (mystr[0]==mystr[len-1]){
        char* newstr;
        int i=0;
        int j=1;
        while(j<len-1){
            newstr[i]=mystr[j];
            i++;
            j++;
        }
        printf("%s", newstr);
        return Palindrome(newstr, len-2);
    }
    else
        printf("Not palindrome");
}

But I am getting this error: Segmentation fault (core dumped)

Why is this?

Answer 1

1. char *newstr is uninitialized which cause your segfault when you deference it.
2. return an int when you declare the function as such.
3. (advise) It's a good idea to terminate lines with a \n.

The way you structured your code I thought you were going for a recursive algorithm:

#include <stdio.h>
#include <string.h>

int Palindrome(char mystr[], size_t len) {
    if(len < 2) {
        printf("Palindrome\n");
        return 1;
    }
    if(mystr[0] != mystr[len-1])
        printf("Not palindrome\n");
        return 0;
    }
    return Palindrome(mystr + 1, len - 2);
}

int main(void) {
    char *test = "racecar";
    Palindrome(test, strlen(test));
}

and the corresponding output is:

Palindrome

Here is how I would write the iterative version:

int Palindrome(char mystr[], int len){
    for(; len > 1; mystr++, len -= 2) {
        if(*mystr != mystr[len - 1]) {
            printf("Not palindrome\n");
            return 0;
        }
    }
    printf("Palindrome\n");
    return 1;
}