转换为浮动和计算 [英] Convert to Float and Calculate

问题描述

我有一个包含多个数字和运算符的字符串

I have a string with multiple digits and operators

@ 5 + 4-9 / 10 。

如何从中得到结果？

我想在我使用的计算器中使用它。我必须在按下数字或运算符时动态显示结果。

I want to use it within the calculator i am using. I will have to display the result dynamically when a digit or operator is pressed.

我在 android 中使用了arity jar文件。但是我无法在 iPhone 中实现类似的功能。

I used arity jar file in android. But i am not able to achieve something like that in iPhone.

推荐答案

这个怎么样 -

NSString *formula = @"1+5*6";
NSExpression *exp = [NSExpression expressionWithFormat:formula];
NSNumber *resultForCustomFormula = [exp expressionValueWithObject:nil context:nil];
NSLog(@"%f", [resultForCustomFormula floatValue]);

编辑：
现在我考虑了你的要求并做了使用 NSScanner的方法在 NSScanner stackoverflow.com/users/1155387/borrrden\">Mr。 Borrrden 建议我使用它，我发现它很棒。见下面的方法 -

EDIT : Now I thought about your requirement and made a method using NSScanner You will not believe I didn't use NSScanner before Mr. Borrrden suggested me to use it and I found it awesome. See below method -

-(NSMutableString *)formatString:(NSString *)formula
{
    // Let's check if there any wrong (.) value exm: 1/.2 or .7+3 
    // 1/0.2 and 0.7+3 are okay but above are incorrect so first fix them

    NSString *str = formula;
    NSInteger c = 0;
    for(int i=0; i<[str length]; i++)
    {

        if([[NSString stringWithFormat:@"%c",[str characterAtIndex:i]] isEqualToString:@"+"] ||
           [[NSString stringWithFormat:@"%c",[str characterAtIndex:i]] isEqualToString:@"-"] ||
           [[NSString stringWithFormat:@"%c",[str characterAtIndex:i]] isEqualToString:@"/"] ||
           [[NSString stringWithFormat:@"%c",[str characterAtIndex:i]] isEqualToString:@"*"])
        {
            if([str length] > i+1)
            {
                if([[NSString stringWithFormat:@"%c",[str characterAtIndex:i+1]] isEqualToString:@"."])
                {
                    formula = [formula stringByReplacingCharactersInRange:NSMakeRange(i+1+c, 1) withString:@"0."];
                    c++;
                }
            }
        }
    }

    // Now we will convert all numbers in float

    NSString *aString;
    float aFloat;
    NSMutableString *formattedString = [[NSMutableString alloc]init];

    NSScanner *theScanner = [NSScanner scannerWithString:formula];
    while ([theScanner isAtEnd] == NO) 
    {

        if([theScanner scanFloat:&aFloat])
        {
            [formattedString appendString:[NSString stringWithFormat:@"%f",aFloat]];
        }

        if([theScanner scanUpToCharactersFromSet:[NSCharacterSet decimalDigitCharacterSet] intoString:&aString])
        {
            [formattedString appendString:aString];
        }
    }
    return formattedString;
}

这将转换（2.222 / .4）+ 9999-7 + 0.7 * .13 输入（2.222000 / 0.400000）+ 9999.000000-7.000000 + 0.700000 * 0.130000 。
在使用 NSExpression 之前调用此方法。

This will convert (2.222/.4)+9999-7+0.7*.13 in to (2.222000/0.400000)+9999.000000-7.000000+0.700000*0.130000.
Just call this method before using NSExpression.

NSString *formula = @"(2.222/.4)+9999-7+0.7*.13";
NSString *formattedString = [self formatString:formula];
NSExpression *exp = [NSExpression expressionWithFormat:formattedString];
NSNumber *resultForCustomFormula = [exp expressionValueWithObject:nil context:nil];
NSLog(@"Result = %f", [resultForCustomFormula floatValue]);

//OutPut: Result = 9997.646484

注意：我并不是说它适用于所有公式字符串。可能在某些情况下不起作用。但它适用于一般方程式。

Note: I'm not saying that it will work in all formula strings. May be it will not work in some case. But it will work in general equations.

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