Objective c 比较小数的不同方法_Objective C_Ios_Nsdecimalnumber

Objective c 比较小数的不同方法

objective-c ios

Objective c 比较小数的不同方法,objective-c,ios,nsdecimalnumber,Objective C,Ios,Nsdecimalnumber,例如，对于primitive，我将这样做 if ( (x >= 6000) && (x <= 20000) ) // do something here 有没有其他方法（更简单、更优雅）来进行比较？如果我将值转换为基元，我应该使用什么基元？我不想使用CGFloat、float或double，因为我在这里处理的是货币。或者，如果我将它们转换为上面提到的那些，有人能验证/解释精度吗？我的理解是，您只能使用比较：方法比较NSDecimalNumber和NSNum

例如，对于primitive，我将这样做

if ( (x >= 6000) && (x <= 20000) )
    // do something here

有没有其他方法（更简单、更优雅）来进行比较？如果我将值转换为基元，我应该使用什么基元？我不想使用CGFloat、float或double，因为我在这里处理的是货币。或者，如果我将它们转换为上面提到的那些，有人能验证/解释精度吗？

我的理解是，您只能使用

比较：

方法比较

NSDecimalNumber

和

NSNumber

对象。超级令人沮丧，但我相信它源于Objective-C不支持运算符重载

如果它真的变得很难阅读，你可以添加一个带有一些助手方法的类别来尝试让它更可读，也许像这样

// NSNumber+PrimativeComparison.m

- (NSComparisonResult) compareWithInt:(int)i{
    return [self compare:[NSNumber numberWithInt:i]]
}

- (BOOL) isEqualToInt:(int)i{
    return [self compareWithInt:i] == NSOrderedSame;
}

- (BOOL) isGreaterThanInt:(int)i{
    return [self compareWithInt:i] == NSOrderedDescending;
}

- (BOOL) isGreaterThanOrEqualToInt:(int)i{
    return [self isGreaterThanInt:i] || [self isEqualToInt:i];
}

- (BOOL) isLessThanInt:(int)i{
    return [self compareWithInt:i] == NSOrderedAscending;
}

- (BOOL) isLessThanOrEqualToInt:(int)i{
    return [self isLessThanInt:i] || [self isEqualToInt:i];
}

然后事情变得更人性化：

if([x isGreaterThanOrEqualToInt:6000] && [x isLessThanOrEqualToInt:20000]){
    //...
}

编辑我刚刚注意到，您还询问了为什么在货币方案中使用NSDecimalNumber是最佳选择。给出了一个很好的例子，解释了为什么在使用货币时浮动（和双倍）不够精确。此外，建议您在执行base-10算术时使用它。

如果（[x doubleValue]>=6000.0f）和（[x doubleValue]compare
方法返回sensorderedescing
，sensorderedescing
或sensorderedsame

if(([x doubleValue]>=6000.0f) && ([x doubleValue] <=20000.0f))

相反，你可以很容易地写
if ( 
    [x compare:[NSNumber numberWithInt:6000]] != NSOrderedAscending && 
    [x compare:[NSNumber numberWithInt:20000]] != NSOrderedDescending
)
{
    // do something here
}

可读性稍好。NSDecimalNumber+比较类别代码
良好度量的单元测试
我相信double的精度只有15位左右，而NSDecimalNumber大约是38位。因为他在处理货币问题，所以最好还是谨慎一点，在这里使用最精确的数字表示法。事实上，这更好地解释了浮点（和double）的原因数学不够精确，无法用于货币计算。在本例中，他将其与整数进行比较，因此我认为[x intValue]也可以。这就是所需的精度。如果您需要一个简单的旧整数，为什么要首先使用重量级的NSDecimalNumber？小提示：If（[x compare:[NSNumber numberWithInt:6000]）！=NSorDeredescending）和（[x比较：[NSNumber Withint:20000]]！=NSorDeredescending））给出相同的结果。“大于或等于”等于“不小于”.谢谢！我一直在考虑类似的事情，但老实说，我仍然不喜欢做这个简单的操作有多困难。我关于精度的问题更像是，如果我将它们转换为原语以进行比较，是否有人可以证明它在精度方面是安全的。CGFloat是用二进制格式表示的，w这在处理钱的时候不是很精确。谢谢！
if ( 
    [x compare:[NSNumber numberWithInt:6000]] != NSOrderedAscending && 
    [x compare:[NSNumber numberWithInt:20000]] != NSOrderedDescending
)
{
    // do something here
}

@interface NSDecimalNumber (Comparison)

- (BOOL)isLessThan:(NSDecimalNumber *)decimalNumber;
- (BOOL)isLessThanOrEqualTo:(NSDecimalNumber *)decimalNumber;
- (BOOL)isGreaterThan:(NSDecimalNumber *)decimalNumber;
- (BOOL)isGreaterThanOrEqualTo:(NSDecimalNumber *)decimalNumber;
- (BOOL)isEqualToDecimalNumber:(NSDecimalNumber *)decimalNumber;

@end

@implementation NSDecimalNumber (Comparison)

- (BOOL)isLessThan:(NSDecimalNumber *)decimalNumber
{
    return [self compare:decimalNumber] == NSOrderedAscending;
}

- (BOOL)isLessThanOrEqualTo:(NSDecimalNumber *)decimalNumber
{
    return [self compare:decimalNumber] != NSOrderedDescending;
}

- (BOOL)isGreaterThan:(NSDecimalNumber *)decimalNumber
{
    return [self compare:decimalNumber] == NSOrderedDescending;
}

- (BOOL)isGreaterThanOrEqualTo:(NSDecimalNumber *)decimalNumber
{
    return [self compare:decimalNumber] != NSOrderedAscending;
}

- (BOOL)isEqualToDecimalNumber:(NSDecimalNumber *)decimalNumber
{
    return [self compare:decimalNumber] == NSOrderedSame;
}

@end

@interface NSDecimalNumber_Comparison_Tests : XCTestCase

@end


@implementation NSDecimalNumber_Comparison_Tests

#pragma mark - isLessThan: tests

- (void)test_isLessThan_whenGreaterThan_returnsNO
{
    NSDecimalNumber *decimalNumberA = [NSDecimalNumber decimalNumberWithString:@"4.6780"];
    NSDecimalNumber *decimalNumberB = [NSDecimalNumber decimalNumberWithString:@"4.6779"];

    BOOL result = [decimalNumberA isLessThan:decimalNumberB];

    XCTAssertFalse(result);
}

- (void)test_isLessThan_whenLessThan_returnsYES
{
    NSDecimalNumber *decimalNumberA = [NSDecimalNumber decimalNumberWithString:@"4.6780"];
    NSDecimalNumber *decimalNumberB = [NSDecimalNumber decimalNumberWithString:@"4.6781"];

    BOOL result = [decimalNumberA isLessThan:decimalNumberB];

    XCTAssertTrue(result);
}

- (void)test_isLessThan_whenEqualTo_returnsNO
{
    NSDecimalNumber *decimalNumberA = [NSDecimalNumber decimalNumberWithString:@"4.6780"];
    NSDecimalNumber *decimalNumberB = [NSDecimalNumber decimalNumberWithString:@"4.6780"];

    BOOL result = [decimalNumberA isGreaterThan:decimalNumberB];

    XCTAssertFalse(result);
}

#pragma mark - isLessThanOrEqualTo: tests

- (void)test_isLessThanOrEqualTo_whenGreaterThan_returnsNO
{
    NSDecimalNumber *decimalNumberA = [NSDecimalNumber decimalNumberWithString:@"4.6780"];
    NSDecimalNumber *decimalNumberB = [NSDecimalNumber decimalNumberWithString:@"4.6779"];

    BOOL result = [decimalNumberA isLessThanOrEqualTo:decimalNumberB];

    XCTAssertFalse(result);
}

- (void)test_isLessThanOrEqualTo_whenLessThan_returnsYES
{
    NSDecimalNumber *decimalNumberA = [NSDecimalNumber decimalNumberWithString:@"4.6780"];
    NSDecimalNumber *decimalNumberB = [NSDecimalNumber decimalNumberWithString:@"4.6781"];

    BOOL result = [decimalNumberA isLessThanOrEqualTo:decimalNumberB];

    XCTAssertTrue(result);
}

- (void)test_isLessThanOrEqualTo_whenEqualTo_returnsYES
{
    NSDecimalNumber *decimalNumberA = [NSDecimalNumber decimalNumberWithString:@"4.6780"];
    NSDecimalNumber *decimalNumberB = [NSDecimalNumber decimalNumberWithString:@"4.6780"];

    BOOL result = [decimalNumberA isLessThanOrEqualTo:decimalNumberB];

    XCTAssertTrue(result);
}

#pragma mark - isGreaterThan: tests

- (void)test_isGreaterThan_whenGreaterThan_returnsYES
{
    NSDecimalNumber *decimalNumberA = [NSDecimalNumber decimalNumberWithString:@"4.6780"];
    NSDecimalNumber *decimalNumberB = [NSDecimalNumber decimalNumberWithString:@"4.6779"];

    BOOL result = [decimalNumberA isGreaterThan:decimalNumberB];

    XCTAssertTrue(result);
}

- (void)test_isGreaterThan_whenLessThan_returnsNO
{
    NSDecimalNumber *decimalNumberA = [NSDecimalNumber decimalNumberWithString:@"4.6780"];
    NSDecimalNumber *decimalNumberB = [NSDecimalNumber decimalNumberWithString:@"4.6781"];

    BOOL result = [decimalNumberA isGreaterThan:decimalNumberB];

    XCTAssertFalse(result);
}

- (void)test_isGreaterThan_whenEqualTo_returnsNO
{
    NSDecimalNumber *decimalNumberA = [NSDecimalNumber decimalNumberWithString:@"4.6780"];
    NSDecimalNumber *decimalNumberB = [NSDecimalNumber decimalNumberWithString:@"4.6780"];

    BOOL result = [decimalNumberA isGreaterThan:decimalNumberB];

    XCTAssertFalse(result);
}

#pragma mark - isGreaterThanOrEqualTo: tests

- (void)test_isGreaterThanOrEqualTo_whenGreaterThan_returnsYES
{
    NSDecimalNumber *decimalNumberA = [NSDecimalNumber decimalNumberWithString:@"4.6780"];
    NSDecimalNumber *decimalNumberB = [NSDecimalNumber decimalNumberWithString:@"4.6779"];

    BOOL result = [decimalNumberA isGreaterThanOrEqualTo:decimalNumberB];

    XCTAssertTrue(result);
}

- (void)test_isGreaterThanOrEqualTo_whenLessThan_returnsNO
{
    NSDecimalNumber *decimalNumberA = [NSDecimalNumber decimalNumberWithString:@"4.6780"];
    NSDecimalNumber *decimalNumberB = [NSDecimalNumber decimalNumberWithString:@"4.6781"];

    BOOL result = [decimalNumberA isGreaterThanOrEqualTo:decimalNumberB];

    XCTAssertFalse(result);
}

- (void)test_isGreaterThanOrEqualTo_whenEqualTo_returnsYES
{
    NSDecimalNumber *decimalNumberA = [NSDecimalNumber decimalNumberWithString:@"4.6780"];
    NSDecimalNumber *decimalNumberB = [NSDecimalNumber decimalNumberWithString:@"4.6780"];

    BOOL result = [decimalNumberA isGreaterThanOrEqualTo:decimalNumberB];

    XCTAssertTrue(result);
}

#pragma mark - isEqualToDecimalNumber: tests

- (void)test_isEqualToDecimalNumber_whenGreaterThan_returnsNO
{
    NSDecimalNumber *decimalNumberA = [NSDecimalNumber decimalNumberWithString:@"4.6780"];
    NSDecimalNumber *decimalNumberB = [NSDecimalNumber decimalNumberWithString:@"4.6779"];

    BOOL result = [decimalNumberA isEqualToDecimalNumber:decimalNumberB];

    XCTAssertFalse(result);
}

- (void)test_isEqualToDecimalNumber_whenLessThan_returnsNO
{
    NSDecimalNumber *decimalNumberA = [NSDecimalNumber decimalNumberWithString:@"4.6780"];
    NSDecimalNumber *decimalNumberB = [NSDecimalNumber decimalNumberWithString:@"4.6781"];

    BOOL result = [decimalNumberA isEqualToDecimalNumber:decimalNumberB];

    XCTAssertFalse(result);
}

- (void)test_isEqualToDecimalNumber_whenEqualTo_returnsYES
{
    NSDecimalNumber *decimalNumberA = [NSDecimalNumber decimalNumberWithString:@"4.6780"];
    NSDecimalNumber *decimalNumberB = [NSDecimalNumber decimalNumberWithString:@"4.6780"];

    BOOL result = [decimalNumberA isEqualToDecimalNumber:decimalNumberB];

    XCTAssertTrue(result);
}

@end