CODEWITHSUNDEEP
cpointerssyntax
user3397709
user3397709

Reputation: 1

C Program Syntax (not compiling)

bst.c

//my bst.c
#include <stdio.h>
#include <stdlib.h>
#include "bst.h"
// Input: 뭩ize? size of an array
// Output: a pointer to an allocated array
// Effect: dynamically allocate an array of size+1 float-point numbers
//         the first slot of the array contains size+0.5
//         all the other slots contain -1;
BStree bstree_ini(int size) {
     int * BStree;
     BStree = (int *) malloc ((size+1)*sizeof(float)); //?
     BStree[0]=size+0.5; //?????
     int i;
     for (i=0; i<size; i++){
         BStree[i]=-1;
     }
     return *BStree;
}

bst.h

This header is provided by the professor and cannot be changed.

typedef float* BStree;
const float my_epsilon = 0.0001;
BStree bstree_ini(int size);
void bstree_insert(BStree bst, float key);
void bstree_traversal(BStree bst);
void bstree_free(BStree bst);

Problem

When I compile, it gives me this error: http://puu.sh/7y0Lp.png (the error is within the return statement for my first function). Does anyone know how to fix this? I apologize for posting a very simple question haha, I'm still quite new to C and pointers!

Rest of the code

Here's the rest of the bst.c that I haven't yet finished.

// Input: 뭕st? a binary search tree
// 뭟ey? a non-negative floating-point number
// Effect: key is inserted into bst if it is not already in bst
void bstree_insert(BStree bst, float key) {

}
// Input: 뭕st? a binary search tree
// Effect: print all the numbers in bst using in order traversal
void bstree_traversal(BStree bst) {

}
// Input: 뭕st? a binary search tree
// Effect: memory pointed to by bst is freed
void bstree_free(BStree bst) {

}

Upvotes: 0

Views: 136

Answers (3)

beardhatcode
beardhatcode

Reputation: 4773

You say typedef float* BStree; which means that BStree 'objects' are actually pointers. The warning is due to the fact that you returned an int pointer while the compiler expected a float pointer (== BSTree)

BStree bstree_ini(int size) {
  BStree tree;
  tree = (BStree) malloc ((size+1)*sizeof(float)); /* Make size +1 places to store a float */ 
  tree[0]=0.5 + (float)size; /* cast size to float */
  int i;
  for (i=1; i<=size; i++){ /*you need to start at 1 or you'll overwrite size+0.5*/
      tree[i]=-1.0; 
  }
  return tree; /* returning a pointer to a float* (or a BSTree)*/
}

Note that I did not dereference tree; it is already a pointer

Upvotes: 1

SzG
SzG

Reputation: 12629

Your functions prototype says it returns something with TYPE BStree, which is pointer to a float, but you try to return an integer that VARIABLE BStree is pointing to.

So you return an int instead of a pointer to a float.

BStree bstree_ini(int size) {
    ...
    return *BStree;
}

You call both a type and a variable BStree. That's extremely confusing. Fix that first.

Upvotes: 1

Jonathan Leffler
Jonathan Leffler

Reputation: 754730

The first visible definition is confused, if not confusing:

BStree bstree_ini(int size) {
     int * BStree;

The first line says that bstree_ini() is a function that takes an int argument and returns a BStree.

The second line says that BStree is a local variable of type int *.

You can't have both at once. Since you return *BStree, the local variable is of the wrong type.

Second attempt

Since bstree_ini() needs to return a pointer to an array of floats, you can write:

BStree bstree_ini(int size)
{
     BStree;
     BStree data = malloc ((size + 1) * sizeof(*data));
     data[0] = size + 0.5;
     for (int i = 1; i <= size; i++)
         data[i] = -1.0;
     return data;
}

I remain to be convinced by the design, but given that you can't change the header, this should do the trick for you.

First attempt

This was provided as a possible answer before the confession that the header can't be changed.

The header defines:

typedef float *BStree;

which is a type I would not expect you to be using. You would normally be using a structure type:

typedef struct BStree
{
    float      value;
    struct BStree *l_child;
    struct BStree *r_child;
} BStree;

In your function, you'd then have:

BStree *bstree_ini(int size)
{
    BStree *bp = …;
    …
    return bp;
}

Upvotes: 0

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