problem in my code please help

Question

please help !!!
when i call this function with correct arguments i.e those present in the linked list this works but when i call it with something that is not in list it crashes rather than returning false;
bool validate(string a ,string b,string c)
{

node *temp = head;

while(temp!=NULL)
{

while(temp->username!=a)
{
temp=temp->next;
}
if(temp->password!=b)
{
temp = temp->next;
}
else if(temp->type!=c)
{
temp = temp->next;
}
else
{
if(temp == NULL)
{
return false;
}
return true;
}
}

}

Answer 1

What if the nested while loop ends up not matching temp->username with a and it continues till the node is assigned NULL, after this you'd try to access data from a NULL node,this will make your program crush.
Provide an exception mechanism in the nested while loop to check if temp==NULL,if it is return false.

Answer 2

thank you your answer really helped!