An unfamiliar way to initialize structure array

InitializeStruct.m

typedef struct demoStruct {
    int val;
    float *point; 
} DemoStruct;

@implementation InitStructureAppDelegate


@synthesize window=_window;

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    
    float a = 1.0f;
    float b = 2.0f;
    float c =  3.0f;
    
    DemoStruct demos[4] = {
        {.val = 1, .point = &a},
        {.val = 2},        
        {.point = &b},
        {.val = 3, .point = &c},
    };
    
    for (int i = 0; i < 4; i++)
    {
        printf("%d %f\n", demos[i].val, (demos[i].point ? *(demos[i].point) : -1.0f));
    }
    
    // Override point for customization after application launch.
    [self.window makeKeyAndVisible];
    return YES;
}