Program doesn't wait for user input!

[gaurav_13191]

Hi, I am trying to make a program that finds the Nth node in the linked list where N is user input. When the user adds the element in the linked list, after each addition I ask whether to continue addition or stop. Here the user is expected to enter Y/N as his choice but the program skips this portion and doesn't wait for user input here.

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

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

struct node *addElement(struct node *headPtr,int elem); 
int lengthList(struct node *headPtr);
int Find_Nth_Node(struct node *headPtr,int number);

int main()
{
	int num,temp,value;
	char choice;
	struct node *front=NULL;
	
	/*printf("Enter number of nodes:");
	scanf("%d",&num);*/
        choice='y';
	printf("\nEnter elements:\n");
	while(choice=='y'||choice=='Y')
	{
		scanf("%d",&temp);
		front=addElement(front,temp);
		printf("\nWant to enter more?");
		scanf("%c",&choice);         //doesn't wait for user input
	}

	printf("\nEnter the number of node whose value is desired:");
	scanf("%d",&num);
	if(num>lengthList(front))
	{
		printf("\nSorry, there are less than %d nodes in the list",num);
		return 0;
	}
	value=Find_Nth_Node(front,num);

	printf("\nThe value at node %d is:%d",num,value);
	getchar();
	return 0;
}

struct node *addElement(struct node *headPtr,int elem)
{
	struct node *trav_ptr,*temp;
	temp=(struct node *)malloc(sizeof(struct node));
	if(temp==NULL)
	{
		printf("\nError, no free space");
		return 0;
	}
	else
	{
		temp->nodeValue=elem;
		temp->link=NULL;
	}
     
if(headPtr==NULL)											       	                                    //If linked list is empty
		headPtr=temp;
	else																		//If linked list is not empty
	{
		trav_ptr=headPtr;
		while(trav_ptr->link!=NULL)
			trav_ptr=trav_ptr->link;
		trav_ptr->link=temp;
	}
	return headPtr;
}

int lengthList(struct node *headPtr)
{
	int length=1;
	while(headPtr->link!=NULL)
	{
		headPtr=headPtr->link;
		length++;
	}
	return length;
}

int Find_Nth_Node(struct node *headPtr,int number)
{
	int ctr=0;
	while(ctr++<number)
		headPtr=headPtr->link;
	return headPtr->nodeValue;
}

Waiting for some suggestions.

[Salem]

All the basic format conversions (except %c) skip white space and newlines.
%c is different, it unconditionally reads the next character.

In your code, this will typically be the \n left at the end of the previous %d.

You could read this -> Cprogramming.com FAQ > Flush the input buffer

Or you could use fgets() to read ALL input into a buffer, then use whatever (perhaps sscanf) to get from the buffer whatever interests you.

[gaurav_13191]

Thanks for the suggestion, you are right, the choice variable was taking newline as the input and continuing the execution without user input. So i flushed the input buffer and now the program works as intended.

[Blane]

I see, so the %c will actually read in the "Enter" key from the %d above?

[gaurav_13191]

Yes, I debugged the program and choice variable contained ASCII 10(Linefeed) that caused the program to produce mysterious results.

[CommonTater]

Thanks for the suggestion, you are right, the choice variable was taking newline as the input and continuing the execution without user input. So i flushed the input buffer and now the program works as intended.

Quick and easy fix...

scanf(" %c",&ch);

Note the space inserted between the " and the %.

[Blane]

Quick and easy fix...

scanf(" %c",&ch);

Note the space inserted between the " and the %.

I almost forgot about this method,
every time I encounter that problem I just use fflush(stdin) .

any difference by using fflush or add blackspace behind it?

[CommonTater]

I almost forgot about this method,
every time I encounter that problem I just use fflush(stdin) .

any difference by using fflush or add blackspace behind it?

Unless you're using that braindead old Turbo C or Turbo C++ compiler fflush(stdin) is some serious bad juju... that can cause data loss on buffered input streams.

[AndrewHunter]

any difference by using fflush or add blackspace behind it?

After an exhaustive internet search, making multiple phone calls, and then writing a few letters; I was rewarded with this little gem hidden away by the all powerful mods to ensure us mere mortals would never find it:

FAQ-fflush(stdin)