Почему переменные в созданном классе не отображаются в main()?

#import <Foundation/Foundation.h>

@interface StockHolding : NSObject
{
    float purchaseSharePrice;
    float currentSharePrice;
    int numberOfShares;
}

@property float purchaseSharePrice;
@property float currentSharePrice;
@property int numberOfShares;

- (float)costInDollars;
- (float)valueInDollars;

@end

#import "StockHolding.h"

@implementation StockHolding

@synthesize purchaseSharePrice, currentSharePrice, numberOfShares;

- (float)costInDollars
{
    return purchaseSharePrice * numberOfShares;
}

- (float)valueInDollars
{
    return currentSharePrice * numberOfShares;
}
@end

#import <Foundation/Foundation.h>
#import "StockHolding.h"

int main(int argc, const char * argv[])
{

    @autoreleasepool {
        
        NSArray *threeobjects = [NSArray arrayWithObjects:purchaseSharePrice, currentSharePrice, numberOfShares, nil];
        
    }
    return 0;
}