问题描述
我试图在程序中递归添加一些CGFloat值。我刚刚在一个特定情况下意识到生成的总数是不正确的。为了确保我的程序逻辑没有任何问题，我创建了一个该场景的简单示例（见下文），并打印出相同的错误值。
I was trying to add some CGFloat values recursively in my program. And I just realized in one particular scenario the total generated was incorrect. To ensure I had nothing wrong in my program logic, I created a simple example of that scenario (see below) and this printed the same wrong value.
CGFloat arr[3] = {34484000,512085280,143011440};
CGFloat sum = 0.0;
sum = arr[0] + arr[1] + arr[2];
NSLog(@"%f",sum);
int arr1[3] = {34484000,512085280,143011440};
int sum1 = 0.0;
sum1 = arr1[0] + arr1[1] + arr1[2];
NSLog(@"%d",sum1);
第一个NSLog打印689580736.000000 ...而正确的结果是689580720.但是第二个NSLog打印正确结果。我不确定这是一个错误还是我做错了。
The first NSLog prints 689580736.000000...while the correct result 689580720. However the second NSLog prints the correct result. I am not sure if this is a bug or if I am doing something wrong.
谢谢，
Murali
Thanks,Murali
推荐答案
CGFloat 是32位目标（如iOS）上的单精度浮点数 - 它只有23位尾数，即大约6 - 7位数。如果您需要更高的准确度，请使用双精度类型。
CGFloat is a single precision float on 32 bit targets such as iOS - it only has a 23 bit mantissa, i.e. around 6 - 7 significant digits. Use a double precision type if you need greater accuracy.
您应该阅读David Goldberg的，然后再继续学习编程。
You should probably read David Goldberg's What Every Computer Scientist Should Know About Floating-Point Arithmetic before proceeding much further with learning to program.
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