Thread: Segmentation fault

Here is my code.

While debugging i found out that a segmentation fault error while the third element 6 is added.

Code:

#include <stdio.h>
#include <stdlib.h>

struct node {
    int data;
    struct node *link;
};

void display(struct node *q) {
    while(q != NULL) {
        printf("%d ",q -> data);
        q = q -> link;
    }
}

int count(struct node *q) {
    int c = 0;

    while(q != NULL) {
        c++;
        q = q -> link;
    }
    return c;
}

void add(struct node **q,int num) {
    struct node *r,*temp = *q;
    r = (struct node *)malloc(sizeof(struct node));
    r -> data = num;

    if(*q == NULL || num < (*q) -> data) {
        *q = r;
        r -> link = temp;
    }
    else {
        while(temp != NULL) {
            if(num >= temp -> data && (num < temp -> link -> data || temp -> link == NULL)) {
                r -> link = temp -> link;
                temp -> link = r;
                return;
            }
            temp = temp -> link;
        }
    }
}

int main() {
    struct node *p = NULL;

    add(&p,5);
    add(&p,1);
    add(&p,6);
    add(&p,4);
    add(&p,7);

    display(p);
}

Please help guys