list of pairs on integers

[jacek]

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

typedef struct node {
  int a;
  int b;
  struct node *next;
} *list;

void print(list head);

int main()
{
  list ptr, new ;
  int n;
  
  ptr=NULL;
  new = malloc(sizeof(struct node));
  new->a = 1;
  new->b = 2;
  new->next = NULL;
  printf ("Enter both integers separated by a space.\nIf you want to stop, write everything but integers.\n");

do {
n = scanf("%d %d", &new->a, &new->b);
if (n != 2) {
printf("You must write integers only\n");
return 1;
}
}
while (n==2);

printf("Integers you entered: %d %d", new->a, new->b);
return 0;


   print(ptr);
}



void print(list head) { 
    list curr; 
    int i=0; 
    curr=head;
 
    printf("Printing the list:\n"); 
    while(curr) { 
        printf("%d\n", curr->a);
	 printf("%d\n", curr->b);
        curr=curr->next; 
        i++; 
    } 
    printf("Printed %d elements\n", i); 
}

Could you tell my why void function is not working here?

[nadroj]

Well you never said what you mean by "not working". If you mean "not being executed", then

printf("Integers you entered: %d %d", new->a, new->b);
return 0;


   print(ptr);

You return before you have a chance to call it. If you turn up your compilers warning level, then you would have got a message saying this. Whether your function actually "works" or not is a different story (I havent looked at it either).

[jacek]

ok, it executes.

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

typedef struct node {
  int a;
  int b;
  struct node *next;
} *list;

void print(list head);

int main()
{
  list ptr, new ;
  int n;
  
  ptr=NULL;
  new = malloc(sizeof(struct node));
  new->a = 1;
  new->b = 2;
  new->next = NULL;
  printf ("Enter both integers separated by a space.\nIf you want to stop, write everything but integers.\n");

  n = scanf("%d %d", &new->a, &new->b);
  if (n != 2) {
    printf("You must write integers only\n");
    return 1;
  }

  /*printf("Integers you entered: %d %d\n", new->a, new->b);*/

  print(new);

  return 0;
}



void print(list head) { 
    list curr; 
    int i=0; 
    curr=head;
 
    printf("Printing the list:\n"); 
    while(curr) { 
        printf("%d\n", curr->a);
	 printf("%d\n", curr->b);
        curr=curr->next; 
        i++; 
    } 
    printf("Printed %d elements\n", i); 
}

However it asks me about only one pair - how to make it asking for more?

[nadroj]

In your first code that you posted you have a do-while loop (in main), but in your new code there is no do-while loop (in main), so certainly will only ask one time. You probably removed that loop when you were debugging and forgot to put it back in. Put your first one back in.

[jacek]

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

typedef struct node {
  int a;
  int b;
  struct node *next;
} *list;

void print(list head);

int main()
{
  list ptr, new ;
  int n;
  
  ptr=NULL;
  new = malloc(sizeof(struct node));
  new->a = 1;
  new->b = 2;
  new->next = NULL;
  printf ("Enter both integers separated by a space.\nIf you want to stop, write everything but integers.\n");

  do {
  n = scanf("%d %d", &new->a, &new->b);
  if (n != 2) {
    printf("You must write integers only\n");
    return 1;
    		}
     }
while (n==2);


  /*printf("Integers you entered: %d %d\n", new->a, new->b);*/

  print(new);

  return 0;
}



void print(list head) { 
    list curr; 
    int i=0; 
    curr=head;
 
    printf("Printing the list:\n"); 
    while(curr) { 
        printf("%d\n", curr->a);
	 printf("%d\n", curr->b);
        curr=curr->next; 
        i++; 
    } 
    printf("Printed %d elements\n", i); 
}

ok. however, it doesn't print the content - just writes that I should enter integers only... How to fix it?

[nadroj]

  do {
  n = scanf("%d %d", &new->a, &new->b);
  if (n != 2) {
    printf("You must write integers only\n");
    return 1;
    		}
     }
while (n==2);

The loop continues as long as n is 2, so it stops when is not 2. However, after the scanf you check if n != 2 and if it is you exit ("return" from main). So either the loop continues indefinitely or you read n != 2 tokens and exit the program. So control never reaches past the end of the while loop.

You have this problem because your loop "terminator"/condition is ambiguous. You need to define some other method to tell the program "Im done entering pairs of ints". For example, maybe when only one number is entered and its a '-1' or something. You then know that the user purposely put bad data with the intention of continuing the program. Any other input with n != 2 means bad data. (Use this or any other method you see fit).

Next, your list always only contains one element, so "print" will always only print the last pair of numbers entered. This is because in your while loop your overwriting the pairs of integers a, b each time. You probably want to create a new element and add to the list, rather than overwriting the previous element.

Also, if weird things happen with the input/output, see http://faq.cprogramming.com/cgi-bin/...&id=1043284385. But I think your exact input is ok now.

[jacek]

your list always only contains one element, so "print" will always only print the last pair of numbers entered. This is because in your while loop your overwriting the pairs of integers a, b each time. You probably want to create a new element and add to the list, rather than overwriting the previous element.

This is exaclty what I mean - but how to do it?

[nadroj]

Well if its exactly what you mean then you should fix the previous problems. I doubt its exactly what you mean, because you wouldnt know what it outputs because it never does. So the only way of finding out is by you manually tracing the program, which I highly doubt you did.

Im not going to write the program for you. Look up basic examples of a linked list. You have most of it, you just need a few more lines in your do/while loop (minimum of 2 lines I believe). You need to create a new node and "attach" it to the existing list.

[iMalc]

If you were the one who wrote the print function then you would know how to write the bit you're asking about now. Given that you aren't understanding the basic advice being offered, and fail to recognise why a loop is even necessary to input multiple values, I think you need to go back to other sources such as tutorials and actually learn about what you're doing.

There is no shortcut to learning how to program. "Do or do not; there is no try!"

[jacek]

ok, could you point me to some good tutorials?