Help with Linked Lists

This is a discussion on Help with Linked Lists within the C Programming forums, part of the General Programming Boards category; I'm trying to use a for loop to create new structures of a linked list, but I keep overwriting the ...

  1. #1
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    Apr 2008
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    Help with Linked Lists

    I'm trying to use a for loop to create new structures of a linked list, but I keep overwriting the last struct and I don't know how to fix it.

    Code:
    struct node *make_linked_list(char *pointArray[], int N, int polyNumber) { 
    	struct node *first, *current, *newNode, *o;
    	char *term, *poly, sign = ' ';
    	int i, num;
    
    	poly = pointArray[0];
    	//beginning of the linked list
      	current = calloc(1,sizeof(struct node));
    	first = current;
    	/* Read the first term of the polynomial. From there, a new node will be created
    	 * for each term. Do this for however many polynomials are in the file.
    	 */
    	term = strtok(poly, " ");
            for(i=0; term != NULL; i++) {
    		term = strtok(NULL, " "); 
     .
     .
     .
    		newNode = calloc(1,sizeof(struct node));
    		current->next = newNode;
    		current = current->next;
    return first
    }

  2. #2
    Algorithm Dissector iMalc's Avatar
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    It does not help when you leave out the bit that probably has the bug in it. You're missing a bracket too.
    If you want real help you have to post the real code.
    My homepage
    Advice: Take only as directed - If symptoms persist, please see your debugger

    Linus Torvalds: "But it clearly is the only right way. The fact that everybody else does it some other way only means that they are wrong"

  3. #3
    Registered User
    Join Date
    Apr 2008
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    31
    I figured out how to create a linked list. Now I'm having a problem with a while loop that adds 2 polynomials together. Everything seems to work correctly up until exiting where the loop checks the condition after the last term of the polynomial and then blows up.
    Code:
    struct node *add(struct node *head1, struct node *head2) { //Use only for ordered lists
    	struct node *poly_a, *poly_b, *sum, *tsum;
    
    	poly_a = head1;
    	poly_b = head2;
    	sum = calloc(1,sizeof(struct node));
    	sum->next = calloc(1,sizeof(struct node));
    	tsum = sum;
    	while(poly_a->next != NULL || poly_b->next != NULL) {
    		/* If a term is present in the first polynomial and not the second,
    		 * copy coeff and exp into the sum polynomial structure.
    		 */
    		if(poly_a->exp > poly_b->exp) {
    			tsum->exp = poly_a->exp;
    			tsum->coeff = poly_a->coeff;
    			poly_a = poly_a->next;
    			tsum->next = calloc(1,sizeof(struct node));
    			tsum = tsum->next;
    			continue;
    		}
    		/* If a term is present in the second polynomial and not the first,
    		 * copy coeff and exp into the sum polynomial structure.
    		 */
    		else if(poly_b->exp > poly_a->exp) {
    			tsum->exp = poly_b->exp;
    			tsum->coeff = poly_b->coeff;
    			poly_b = poly_b->next;
    			tsum->next = calloc(1,sizeof(struct node));
    			tsum = tsum->next;
    			continue;
    		}
    		/* If a term is present in both polynomials, add coefficients and copy exp into the sum 
    		 * polynomial structure.
    		 */
    		else if(poly_b->exp == poly_a->exp) {
    			tsum->exp = poly_b->exp;
    			tsum->coeff = poly_b->coeff + poly_a->coeff;
    			tsum->next = calloc(1,sizeof(struct node));
    			tsum = tsum->next;
    			poly_b = poly_b->next;
    			poly_a = poly_a->next;
    		}
    
    	}
    	return sum;
    }
    Last edited by arrgh; 04-17-2008 at 03:53 AM.

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