在iOS 7.1应用程序Xcode 5.1中获取数字百分比时遇到问题

Question

In my iOS 7.1 application that I'm trying to develop, I need to figure out percentages of a specific number which is entered in a UITextField. It would appear when executing the code I get the wrong percentage of that number entered.

I've tried two different ways to get the require percentage answer I'm looking for, however it keeps giving the wrong answer.

Below here is the two methods that I've tried.

For example I want to get 72% of 250. If you were to do this on a calculator or better yet a excel spreadsheet I get the right answer 250 x 1 - 72% = 70. This is the correct answer I want

Method1 (.m file) Not working

Values that are set the the specific .text parameters:

Entered in the UITextField _linuxOracleOnDiskw_oRTC.text = 250
Value set to UITextField _formulaNumber.text = 1
Percentage Value set to _linuxOracle_Percent.text = 0.72 

_linuxOracleOnDiskwithRTC.text = [NSString stringWithFormat:@"%.2f", ([_linuxOracleOnDiskw_oRTC.text doubleValue])*([_formulaNumber.text doubleValue])-([_linuxOracle_Percent.text doubleValue])];

When executed I the answer or vale that gets entered in the UITextField _linuxOracleOnDiskwithRTC.text is 249.28. This is wrong should be 70

Second method tried is as follows:

float linuxOracleOnDiskw_oRTC = [_linuxOracleOnDiskw_oRTC.text floatValue];

_linuxOracleOnDiskwithRTC.text = [NSString stringWithFormat:@"%.2f", (linuxOracleOnDiskw_oRTC * 1 - 72/100.0f )];

If someone can tell me what I maybe doing wrong and point me in the right direction with calculating percentages of a specific number entered in a UITextField I would be extremely GREATFUL.

Answer 1

Don't omit your brackets when performing calculations with code. For "250 x 1 - 72%" to get 70, you need to do this:

250 x (1 - 0.72) = 250 x 0.28 = 70

Formulas in () will be calculated first, followed by multiplication and division (whichever first), then followed by addition and subtraction (whichever first). So, insert your brackets appropriately.

Answer 2

Your formula to calculate the percentage is incorrect. One correct way to calculate percentages is

250 / 100 x 72

This gives you 72% of 250. The result of that isn't 70, btw, but 180. If you want 70, then you don't want 72% but 28% (or 100% - 72%):

250 / 100 x (100 - 72)