problem with looping scanf

I'm trying to fix someones code for them but I've got myself stuck.

Code:

---

int main()
{
        float x = 0, temp=0 , high, low;
        int num,i,*ptr,sum = 0,mean;
        char choose;

        printf("This program will ask the user for a list of numbers.\n");
  printf("Then calculate the median or mean average.\n\n");
        printf("How many numbers are you going to put in?\n:  ");
        scanf("%d",&num);

  ptr = (int*) malloc ( num  * sizeof (int));    //Creates enough room for the array
  if (ptr == NULL) printf("Malloc failed");
  for (i=0;i<=num;i++)        {                  //Fills the array with inputted values
      printf("i = %d\n",i);
      scanf("%d",*(ptr + i)); //PROBLEM HERE
      }

---

After I've inputted 3 values ( I should be able to put much more in ) in crashes my dos prompt. Can anyone here see whats wrong?


This isn't full code by the way, if you are wondering why there are lots of unused variables.

Quote:

---

Originally posted by crag2804
I'm trying to fix someones code for them but I've got myself stuck.

Code:

---

int main()
{
        float x = 0, temp=0 , high, low;
        int num,i,*ptr,sum = 0,mean;
        char choose;

        printf("This program will ask the user for a list of numbers.\n");
  printf("Then calculate the median or mean average.\n\n");
        printf("How many numbers are you going to put in?\n:  ");
        scanf("%d",&num);

  ptr = (int*) malloc ( num  * sizeof (int));    //Creates enough room for the array
  if (ptr == NULL) printf("Malloc failed");
  for (i=0;i<=num;i++)        {                  //Fills the array with inputted values
      printf("i = %d\n",i);
      scanf("%d",*(ptr + i)); //PROBLEM HERE
      }

---

After I've inputted 3 values ( I should be able to put much more in ) in crashes my dos prompt. Can anyone here see whats wrong?


This isn't full code by the way, if you are wondering why there are lots of unused variables.

---

stuff:
you didnt return a value from main()
when you allocate space for num ints, your for loop should look like this:
for (i=0;i<num;i++)
how much do you know of pointers? i suggest getting a good book on them. scanf expects a pointer to int arg, which is why with a regular int you take the address of it with the & operator. but why are you indirecting in
scanf("%d",*(ptr + i));
? The indirection operator yields an int from a pointer to an int. but scanf expects a pointer, not an int. so you should just do
scanf("%d", ptr + i);

also, if your malloc () fails, you print the message that it did, but then continue on to access the invalid pointer.

no return-its not the full code.
scanf("%d",*(ptr + i)); I thought was same as
scanf("%d",ptr[i]);
Is it?

Code:

---

ptr = (int*) malloc ( num  * sizeof (int));    //Creates enough room for the array
  if (ptr == NULL) printf("Malloc failed");
  for (i=0;i<num ;i++)        {                  //Fills the array with inputted values
      printf("i = %d\n",i);
      scanf("%d",ptr[i]);
      }

---

I've recompiled as that but it doesn't help still crashes. it doesn't crash if I put 2 values into the array.

Quote:

---

Originally posted by crag2804
no return-its not the full code.
scanf("%d",*(ptr + i)); I thought was same as
scanf("%d",ptr[i]);
Is it?

---

/me taps into final bits of brain power before sleep sets in

why of course it is. but, both expressions *(ptr + i) and ptr[i] yield an int. scanf wants an int *. this is why when you scanfed for num you didnt do

scanf("%d",num);

you did

scanf("%d",&num);

Much in the same way, you need to take the address of the other expression to yield an int *. so:

&ptr[i]

or

&*(ptr + i)

both are valid. but the &* is of course redundant, so that expression is equivalent to

ptr + i

*(ptr + i)
and
ptr[i]

are both the same, but scanf takes a pointer, so if you used the array indexing you would have to use &ptr[i] and if you used pointer notation, which is stupid since array indexing is easier to read, you would have to say either (ptr + i) or &*(ptr + i). Don't forget that you allocated space for 3 integers but your loop goes 4 times. That's an off by one bug, the loop test should be i < num.

Thanks a lot, I guess that's what you get for coding at 3:08am. Seems so simple now.