hashtable not working because of scanf() - c

Question

I'm learning C data structures. I've the following code, which is resulting in a segmentation fault.
I've used the hash function from K&R C (2nd Ed.).
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define HASHSIZE 101
typedef struct Details
{
char *name;
float checkTotal;
float tipTotal;
int numReciepts;
struct Details *next;
struct Details *prev;
} det;
static det *hashtab[HASHSIZE];
char *str_dup(char *);
det *lookup(char *);
det *insert(char *, float, float);
unsigned hash(char *);
void printData(char *);
int main()
{
printf("1. Enter details.\n");
printf("2. Print List of employees.\n");
char *s;
float cT; //checkTotal
float tT; //tipTotal
while (1)
{
int command = 0;
printf("Enter option: ");
scanf("%d", &command);
if (command == 1)
{
printf("Enter name: ");
scanf("%s", s);
printf("Enter check total: ");
scanf("%f", &cT);
printf("Enter tip total: ");
scanf("%f", &tT);
insert(s, cT, tT);
}
else if (command == 2)
{
char *p;
printf("Enter name of employee: ");
scanf("%s", p); //including this line causes seg fault.
printData(p);
}
else
break;
}
return 0;
}
unsigned hash(char *s)
{
unsigned hashval;
for (hashval = 0; *s != '\0'; *s++)
hashval = *s + 31 * hashval;
return hashval % HASHSIZE;
}
det *lookup(char *name)
{
det *ptr;
for (ptr = hashtab[hash(name)]; ptr != NULL; ptr = ptr->next)
{
if (strcmp(name, ptr->name) == 0)
return ptr;
}
return NULL;
}
det *insert(char *name, float cT, float tT)
{
det *new;
unsigned hashval;
if ((new = lookup(name)) == NULL)
{
new = (det *)malloc(sizeof(new));
if (new == NULL || (new->name = str_dup(name)) == NULL)
return NULL;
hashval = hash(name);
new->next = hashtab[hashval];
hashtab[hashval] = new;
new->checkTotal += cT;
new->tipTotal += tT;
new->numReciepts++;
printf("Details of '%s' inserted.\n", name);
}
else
{
new->checkTotal += cT;
new->tipTotal += tT;
new->numReciepts++;
printf("Details of '%s' updated.\n", name);
}
}
char *str_dup(char *s)
{
char *p;
p = (char *)malloc(strlen(s) + 1);
if (p != NULL)
strcpy(p, s);
return p;
}
void printData(char *p)
{
det *ptr;
if ((ptr = lookup(p)) != NULL)
{
printf("Emplyee Name : %s\n", ptr->name);
printf("Total amount : %6.2f\n", ptr->checkTotal);
printf("Total tip : %6.2f\n", ptr->tipTotal);
printf("Total reciepts: %6.2d\n", ptr->numReciepts);
}
else
{
printf("Employee '%s' does not exist.\n", p);
return;
}
}
Without the inclusion of scanf() in else if:main, every thing works fine. Calling printData() with a hard coded string also works.
Inclusion of scanf() in else if:main results in segmentation fault after prompting for name.
I have tried and can not think of the reason. As far as I know:
my code in if:main is not accessing anything in else if:main.
if should not break because of something wrong in else if even if it is wrong. (at least in this scenario, or as far as my understanding goes)
Thanks and any tips for future from experts are appreciated!
P.S: scanf():if is working perfectly.