How do I find the minimum value of a binary tree? - objective-c

Question

I'm trying to find the minimum value of a binary tree. Every time I run my code I get a long 5 digit number like '32675'. I'm pretty sure my understanding of pointers is wrong, but I'm not positive. If I could get some advice I'd really appreciate it. Thanks!
Node definition
#interface Node:NSObject {
#property (nonatomic, strong) Node *left;
#property (nonatomic, strong) Node *right;
#property (nonatomic, assign) int *value;
}
-(id)initWithValue:(int)val {
self = [super init];
if(self) {
self.value = &(val);
self.left = nil;
self.right = nil;
}
return self;
}
Insert Algorithms for Tree
-(void)insertValue:(int)value {
Node *node = [[Node alloc] initWithValue:value];
[self insertNode:node];
}
-(void)insertNode:(Node *)node {
if (root == nil) {
root = node;
} else {
[node insertNode:node];
}
}
Insert Algorithms for Node
-(void)insertNode:(Node *)node{
if (node.value < self.value) {
[self insertOnLeft:node];
} else {
[self insertOnRight:node];
}
}
-(void)insertOnLeft:(Node *)node {
if (self.left == nil) {
self.left = node;
} else {
[self.left insertNode:node];
}
}
-(void)insertOnRight:(Node *)node {
if (self.right == nil) {
self.right = node;
} else {
[self.right insertNode:node];
}
}
3 values go in to my tree:
[tree insertValue:4];
[tree insertValue:6];
[tree insertValue:2];
int min = [tree findMinimum];
Tree's findMinimum method is called
-(int)findMinimum {
assert(root != nil);
return [root findMinimum];
}
Which call's root's findMinimum - root is a node
-(int)findMinimum {
Node *node = self;
int min = 0;
while (node != nil) {
min = *(node.value);
node = node.left;
}
return min;
}

Answer 1

Your are filling your tree not with integers but with stack addresses which are immediately invalid with this code:
self.value = &(val);
Here val is a parameter variable, which will disappear as soon as the method returns. Taking its address should only be done in rare circumstances and that address should never be stored in a location which outlives val.
Change the type of the value property of Node to int and remove the uses of address of (&) and indirection (*) associated with that property.
HTH

Answer 2

The assignment in the initializer of a pointer to the parameter won't work. Unless you have a good reason not to, actually allocate the int into the Node structure by declaring it an int, not an int *. So your initializer will look like this:
-(id)initWithValue:(int)val {
self = [super init];
if(self) {
self.value = val;
}
return self;
}
EDIT If you weren't sorting on insert (which I missed in the OP), you could instead search for the min recursively as follows:
-(int)findMinimum {
if (self.left && self.right)
return MIN([self.left findMinimum], [self.right findMinimum]);
else if (self.left)
return [self.left findMinimum];
else if (self.right)
return [self.right findMinimum];
else
return self.value;
}