using gcc and getting core dumped [duplicate]

hi i was trying to use this function to take out palindromes and make a new string with them but i get core dumped

i don't see any problem with code really it is complicated because i use so many parameters but i don't think that will make it wrong what do you think?

the result should be "noon i 313 a kayak"

char* Palindroms(char* str){        int size = strlen(str);        char *wordptr;       char *revword;       char *stringptr = malloc(size+1);        for(int i = 0;i < size;i++){             int j = 0;             int k = 0;            while(*str != ''){                wordptr[j] = *str++;                i++;            }            while(j != 0){                revword[k] = wordptr[j];                j--;                k++;                }                if(revword = wordptr)                strcpy(stringptr + k,revword);            }            return stringptr;        }int main(){    char string1[] = "yesterday noon i paid 313 shekels for a new kayak";    char *string3 = Palindroms(string1);    printf("%s", string3);    return 0;