[轉]用Objective-C實現簡單的數學字符串公式的計算

好友第一次用寫技術分享，這么多年都沒見他正經的寫點東西。那天突然抬頭問我，Objective-C有沒字符串計算的。我說，沒有。后來他默默實現了，特為他轉發，表示支持。

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Objective-C開發時遇到需要用到字符串公式來計算結果,自己也沒找到哪里可以直接使用字符串數學公式計算公式值,如"(3+2*2+(1+2))*2-1*5+(5/10-10)"字符串,要直接得結果,發現沒轍,索性自己寫一份簡單的解決方法.

直接貼上代碼:

FormulaStringCalcUtility.h

#import <Foundation/Foundation.h>
@interface FormulaStringCalcUtility : NSObject
+ (NSString *)calcComplexFormulaString:(NSString *)formula;
@end

FormulaStringCalcUtility.m

#import "FormulaStringCalcUtility.h"

@implementation FormulaStringCalcUtility

// 字符串加
+ (NSString *)addV1:(NSString *)v1 v2:(NSString *)v2 {
    CGFloat result = [v1 floatValue] + [v2 floatValue];
    return [NSString stringWithFormat:@"%.2f", result];
}

// 字符串減
+ (NSString *)subV1:(NSString *)v1 v2:(NSString *)v2 {
    CGFloat result = [v1 floatValue] - [v2 floatValue];
    return [NSString stringWithFormat:@"%.2f", result];
}

// 字符串乘
+ (NSString *)mulV1:(NSString *)v1 v2:(NSString *)v2 {
    CGFloat result = [v1 floatValue] * [v2 floatValue];
    return [NSString stringWithFormat:@"%.2f", result];
}

// 字符串除
+ (NSString *)divV1:(NSString *)v1 v2:(NSString *)v2 {
    CGFloat result = [v1 floatValue] / [v2 floatValue];
    return [NSString stringWithFormat:@"%.2f", result];
}

// 簡單只包含 + - 的計算
+ (NSString *)calcSimpleFormula:(NSString *)formula {
    
    NSString *result = @"0";
    char symbol = '+';
    
    int len = formula.length;
    int numStartPoint = 0;
    for (int i = 0; i < len; i++) {
        char c = [formula characterAtIndex:i];
        if (c == '+' || c == '-') {
            NSString *num = [formula substringWithRange:NSMakeRange(numStartPoint, i - numStartPoint)];
            switch (symbol) {
                case '+':
                    result = [self addV1:result v2:num];
                    break;
                case '-':
                    result = [self subV1:result v2:num];
                    break;
                default:
                    break;
            }
            symbol = c;
            numStartPoint = i + 1;
        }
    }
    if (numStartPoint < len) {
        NSString *num = [formula substringWithRange:NSMakeRange(numStartPoint, len - numStartPoint)];
        switch (symbol) {
            case '+':
                result = [self addV1:result v2:num];
                break;
            case '-':
                result = [self subV1:result v2:num];
                break;
            default:
                break;
        }
    }
    return result;
}

// 獲取字符串中的后置數字
+ (NSString *)lastNumberWithString:(NSString *)str {
    int numStartPoint = 0;
    for (int i = str.length - 1; i >= 0; i--) {
        char c = [str characterAtIndex:i];
        if ((c < '0' || c > '9') && c != '.') {
            numStartPoint = i + 1;
            break;
        }
    }
    return [str substringFromIndex:numStartPoint];
}

// 獲取字符串中的前置數字
+ (NSString *)firstNumberWithString:(NSString *)str {
    int numEndPoint = str.length;
    for (int i = 0; i < str.length; i++) {
        char c = [str characterAtIndex:i];
        if ((c < '0' || c > '9') && c != '.') {
            numEndPoint = i;
            break;
        }
    }
    return [str substringToIndex:numEndPoint];
}

// 包含 * / 的計算
+ (NSString *)calcNormalFormula:(NSString *)formula {
    NSRange mulRange = [formula rangeOfString:@"*" options:NSLiteralSearch];
    NSRange divRange = [formula rangeOfString:@"/" options:NSLiteralSearch];
    // 只包含加減的運算
    if (mulRange.length == 0 && divRange.length == 0) {
        return [self calcSimpleFormula:formula];
    }
    // 進行乘除運算
    int index = mulRange.length > 0 ? mulRange.location : divRange.location;
    // 計算左邊表達式
    NSString *left = [formula substringWithRange:NSMakeRange(0, index)];
    NSString *num1 = [self lastNumberWithString:left];
    left = [left substringWithRange:NSMakeRange(0, left.length - num1.length)];
    // 計算右邊表達式
    NSString *right = [formula substringFromIndex:index + 1];
    NSString *num2 = [self firstNumberWithString:right];
    right = [right substringFromIndex:num2.length];
    // 計算一次乘除結果
    NSString *tempResult = @"0";
    if (index == mulRange.location) {
        tempResult = [self mulV1:num1 v2:num2];
    } else {
        tempResult = [self divV1:num1 v2:num2];
    }
    // 代入計算得到新的公式
    NSString *newFormula = [NSString stringWithFormat:@"%@%@%@", left, tempResult, right];
    return [self calcNormalFormula:newFormula];
}

// 復雜計算公式計算,接口主方法
+ (NSString *)calcComplexFormulaString:(NSString *)formula {
    // 左括號
    NSRange lRange = [formula rangeOfString:@"(" options:NSBackwardsSearch];
    // 沒有括號進行二步運算(含有乘除加減)
    if (lRange.length == 0) {
        return [self calcNormalFormula:formula];
    }
    // 右括號
    NSRange rRange = [formula rangeOfString:@")" options:NSLiteralSearch range:NSMakeRange(lRange.location, formula.length-lRange.location)];
   // 獲取括號左右邊的表達式
    NSString *left = [formula substringWithRange:NSMakeRange(0, lRange.location)];
    NSString *right = [formula substringFromIndex:rRange.location + 1];
    // 括號內的表達式
    NSString *middle = [formula substringWithRange:NSMakeRange(lRange.location+1, rRange.location-lRange.location-1)];
    // 代入計算新的公式
    NSString *newFormula = [NSString stringWithFormat:@"%@%@%@", left, [self calcNormalFormula:middle], right];
    return [self calcComplexFormulaString:newFormula];
}

@end

使用方法

NSString *result = [FormulaStringCalcUtility calcComplexFormulaString:@"(3+2*2+(1+2))*2-1*5+(5/10-10)"];
結果: result = @"5.5"

 

原文章地址:傳送門