while loop

This is a discussion on while loop within the C Programming forums, part of the General Programming Boards category; why only the first Iteration workin alright ? Code: #include <stdio.h> #include <stdlib.h> struct Node { int val; struct Node ...

  1. #1
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    Sep 2009
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    while loop

    why only the first Iteration workin alright ?


    Code:
    #include <stdio.h>
    #include <stdlib.h>
    
    struct Node
    {
    	int val;
    	struct Node *next;
    } ;
    
    typedef struct Node Node ;
    
    
    	void addNode(Node *head,Node *tail)
    	{
    		Node *current, *temp;
    		char Continue='y';
    		head=(Node*)malloc(sizeof(Node));
    		head->val=1;
    		current=head;
    		do
    		{
    			printf("continue?\n");
    			scanf("%c",&Continue);
    			temp=(Node*)malloc(sizeof(Node));
    			printf("value=?\n");
    			scanf("%d",&(temp->val));
    			current->next=temp;
    			current=current->next;
    		}
    		while(Continue!='n');
    	}
    
    
    
    void main()
    {
    	Node *head=NULL, *tail=NULL;
    
    	addNode(head,tail);
    
    }

    TNX

  2. #2
    Registered User hk_mp5kpdw's Avatar
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    Northern Virginia/Washington DC Metropolitan Area
    Posts
    3,788
    #1
    Code:
    do
    {
        ...
        scanf("%c",&Continue);
        ...
        scanf("%d",&(temp->val));
    }
    while(Continue!='n');
    The problem is that %c in the scanf call will read a newline leftover in the input stream from the previous loops read of the integer value. Simplest solution there is to add a space in front of the %c format specifier which will tell the scanf call to ignore leading whitespace.
    Code:
    scanf(" %c",&Continue);
           ^ there's a space there now

    #2
    Code:
    head=(Node*)malloc(sizeof(Node));
    
    ...
    
    temp=(Node*)malloc(sizeof(Node));
    Avoid casting the return value of the malloc call.


    #3 You should be setting the next pointer of the newly allocated node to null after you create it, also you head node's next pointer.



    #4
    Code:
    void main()
    main returns int not void.



    #5
    Code:
    void addNode(Node *head,Node *tail)
    {
        ...
    }
    
    void main()
    {
    	Node *head=NULL, *tail=NULL;
    
    	addNode(head,tail);
    
    }
    If you expect to actually do anything with those head/tail pointers in main after the call to addNode then you'll need to change your addNode function to accept pointer-to-pointer-to-Node arguments rather than just simple pointer-to-Node arguments.
    "Owners of dogs will have noticed that, if you provide them with food and water and shelter and affection, they will think you are god. Whereas owners of cats are compelled to realize that, if you provide them with food and water and shelter and affection, they draw the conclusion that they are gods."
    -Christopher Hitchens

  3. #3
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    Sep 2009
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    ok... thank you very much !

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