Question

我有一个循环我试图使用NSDecimalNumber值运行，但返回的值始终是相同的。我理解NSDecimalNumber是不可变的，但我最初使用双值，并在最后得到错误的结果，我认为是一些浮点错误/舍入错误。这是代码：

double balanceAmount = loanAmountValue;
        double rtemp = r / (n * 12);
        double intA = balanceAmount * rtemp;
        double principalA = payfinal - intA;
        double principal = balanceAmount - principalA;
        NSDecimalNumber *balDeciminal = (NSDecimalNumber *) [NSDecimalNumber numberWithDouble:balanceAmount];
        NSDecimalNumber *rTempDecimal = (NSDecimalNumber *) [NSDecimalNumber numberWithDouble:rtemp];
        NSDecimalNumber *payFinalDecimal = (NSDecimalNumber *) [NSDecimalNumber numberWithDouble:payfinal];
        NSDecimalNumber *principalDecimal = (NSDecimalNumber *) [NSDecimalNumber numberWithDouble:principalA];
        for (n = n * 12; n != 0; --n) {
            NSDecimalNumber *realBalanceDecimal = [balDeciminal decimalNumberBySubtracting:principalDecimal];

            NSDecimalNumber *interestDecimal = [balDeciminal decimalNumberByMultiplyingBy:rTempDecimal];
            NSDecimalNumber *principalDecimalAmount = [payFinalDecimal decimalNumberBySubtracting:interestDecimal];



        NSString *tempInterest = [NSString stringWithFormat:@"$%@", interestDecimal];
        [interestLabels addObject:tempInterest];
        NSString *tempPrincipal = [NSString stringWithFormat:@"$%@", principalDecimalAmount];
        [pricipalLabels addObject:tempPrincipal];
        NSString *tempBalance = [NSString stringWithFormat:@"$%@", balDeciminal];
        [balanceLabels addObject: tempBalance];
    }
    NSLog(@"%@", balanceLabels);
    NSLog(@"%@", pricipalLabels);
    NSLog(@"%@", interestLabels);

如果NSDecimalNumber不允许我进行这些计算，那么有人会建议其他能够返回准确结果的其他内容吗？

谢谢！

编辑：双重代码

double r = interestAmountValue/200;
    //NSLog(@"%f", r);
    double n = yearAmountValue;
    double rPower = pow(1+r, 0.166666666);
    double tophalf = rPower - 1;
    double nPower = (-12 * n);
    double bothalf = pow(rPower, nPower);
    double bothalffinal = 1 - bothalf;
    double tempfinal = tophalf / bothalffinal;
    double payfinal = loanAmountValue * tempfinal;
    double totalPaymentd = payfinal * n * 12;

    double totalInterestd = totalPaymentd - loanAmountValue;

for (n = n * 12; n != 0; --n) {



        double realBalance = balanceAmount - principalA;
        double interest = balanceAmount * rtemp;
        NSLog(@"%f", interest);
        double principalAmount = payfinal - interest;





        balanceAmount -= principalA;
}

Answer 1

我想知道是什么让你认为将一个双重放入NSDecimalNumber可能会以某种方式创建额外的精度。它在我看来，在循环中你总是做完全相同的计算。

double给出大约15到16个小数的精度。如果您计算贷款30年，由于没有足够的精确度，您不太可能遇到问题。我建议您使用双精度数字发布代码，让人们看看你出错的地方。

Answer 2

需要清理和检查代码：
for循环不会每次迭代产生更改使用调试器找出原因。也许五个变量未被使用的事实是暗示。

未使用以下变量：

intA
principalA
principal
principalDecimal
realBalanceDecimal

Answer 3

您遇到的问题是，您没有检查贷款是否已经结清，而您输入的是负数，这意味着潜在的问题在于付款的扩散。

double loanAmountValue = 100000;
double balanceAmount = loanAmountValue;
double n = 30;
double interestAmountValue = 8;
double r = interestAmountValue/1200;
double rtemp = r/(n*12);
double intA = balanceAmount * rtemp;


//NSLog(@"%f", r);
double rPower = pow(1+r, 0.166666666);
double tophalf = rPower - 1;
double nPower = (-12 * n);
double bothalf = pow(rPower, nPower);
double bothalffinal = 1 - bothalf;
double tempfinal = tophalf / bothalffinal;
double payfinal = loanAmountValue * tempfinal;
double principalA = balanceAmount - intA;
double totalPaymentd = payfinal * n * 12;

double totalInterestd = totalPaymentd - loanAmountValue;

for (n = n * 12; n != 0; --n) {



    double realBalance = balanceAmount - principalA;
    double interest = balanceAmount * rtemp;
    NSLog(@"interest: %f", interest);
    NSLog(@"rtemp: %f",rtemp);
    double principalAmount = payfinal - interest;



    // Check for negative balance
    if (balanceAmount < principalAmount) {

        NSLog(@"Balance Amount: %f",balanceAmount);
        NSLog(@"Months Left: %f",n);

        break;
    }

    balanceAmount -= principalAmount;


    NSLog(@"balanceAmount %f",balanceAmount);
}

使用n = 30年，loanAmountValue = 100000和interestAmountValue = 8％的代码。我还有63个月的贷款还清了。我假设r = interestAmountValue / 1200而不是200来获得每月的百分比？关于NSDecimal数字的使用，我不知道浮点精度会对你的修正抵押贷款计算器产生什么影响，但你遇到的问题不在于使用双数据类型，而在于付款的扩散。

在for循环中使用NSDecimalNumber？

3 个答案: