Mors Alphabet Segmentation Fault - c

Question

My code doesn't adding second node to tree. It gives me SIGSEGV fault when i'm adding the second node.I think its about strcmp function but when i'm trying to understand how it works properly at the very bottom of main func it returns -1 so i've wrote it like this.And most of my variables named Turkish so here are the translations of them to make you understand more easily
dugum=node,kok=root;sol=left;sag=right;anne=mother
// C program to demonstrate insert operation in binary search tree
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
typedef struct tree {
char *harf;
char *morskodu;
struct tree *left;
struct tree *right;
} agac;
agac *kok = NULL;
void ekle(char *harf, char *morskodu) {
if (kok == NULL) {
kok = (agac *)malloc(sizeof(agac));
kok->harf = harf;
kok->morskodu = morskodu;
kok->left = NULL;
kok->right= NULL;
} else {
agac *yeni = (agac *)malloc(sizeof(agac));
yeni->harf = harf;
yeni->morskodu = morskodu;
yeni->left = NULL;
yeni->right = NULL;
agac *dugum = kok, *anne;
while (dugum != NULL) {
anne = dugum;
if (harf <= dugum->harf)
dugum = dugum->left;
else
dugum = dugum->right;
}
if (harf <= dugum->harf)
anne->left = yeni;
else
anne->right = yeni;
}
}
void dolas(agac *dugum) {
if (dugum != NULL) {
printf(" %s ", dugum->harf);
dolas(dugum->left);
dolas(dugum->right);
}
}
void main() {
ekle("a", "-");
ekle("b", "-.");
dolas(kok);
int x = strcmp("A", "B");
printf("%d", x);
}

Answer 1

You try to dereference a NULL pointer.
while (dugum != NULL) {
anne = dugum;
if (harf <= dugum->harf)
dugum = dugum->sol;
else
dugum = dugum->sag;
}
This loop ends when dugum is NULL.
Directly after you try to access dugum->harf:
if (harf <= dugum->harf)
This leads to undefined behavior.
Also note that this comparisons compare the pointers to string literals, and is therefore also undefined behavior. To compare two C strings you should use strcmp.