# [转]用Objective-C实现简单的数学字符串公式的计算

=================================================

Objective-C开发时遇到需要用到字符串公式来计算结果,自己也没找到哪里可以直接使用字符串数学公式计算公式值,"(3+2*2+(1+2))*2-1*5+(5/10-10)"字符串,要直接得结果,发现没辙,索性自己写一份简单的解决方法.

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];
}

// 字符串减
+ (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];
}

// 简单只包含 + - 的计算
+ (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 '+':
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 '+':
break;
case '-':
result = [self subV1:result v2:num];
break;
default:
break;
}
}
return result;
}

// 获取字符串中的后置数字
+ (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];
}

// 获取字符串中的前置数字
+ (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 * / 的计算
+ (NSString *)calcNormalFormula:(NSString *)formula {
NSRange mulRange = [formula rangeOfString:@"*" options:NSLiteralSearch];
NSRange divRange = [formula rangeOfString:@"/" options:NSLiteralSearch];
// 只包含加减的运算
if (mulRange.length == 0 && divRange.length == 0) {
return [self calcSimpleFormula:formula];
}
// 进行乘除运算
int index = mulRange.length > 0 ? mulRange.location : divRange.location;
// 计算左边表达式
NSString *left = [formula substringWithRange:NSMakeRange(0, index)];
NSString *num1 = [self lastNumberWithString:left];
left = [left substringWithRange:NSMakeRange(0, left.length - num1.length)];
// 计算右边表达式
NSString *right = [formula substringFromIndex:index + 1];
NSString *num2 = [self firstNumberWithString:right];
right = [right substringFromIndex:num2.length];
// 计算一次乘除结果
NSString *tempResult = @"0";
if (index == mulRange.location) {
tempResult = [self mulV1:num1 v2:num2];
} else {
tempResult = [self divV1:num1 v2:num2];
}
// 代入计算得到新的公式
NSString *newFormula = [NSString stringWithFormat:@"%@%@%@", left, tempResult, right];
return [self calcNormalFormula:newFormula];
}

// 复杂计算公式计算,接口主方法
+ (NSString *)calcComplexFormulaString:(NSString *)formula {
// 左括号
NSRange lRange = [formula rangeOfString:@"(" options:NSBackwardsSearch];
// 没有括号进行二步运算(含有乘除加减)
if (lRange.length == 0) {
return [self calcNormalFormula:formula];
}
// 右括号
NSRange rRange = [formula rangeOfString:@")" options:NSLiteralSearch range:NSMakeRange(lRange.location, formula.length-lRange.location)];
// 获取括号左右边的表达式
NSString *left = [formula substringWithRange:NSMakeRange(0, lRange.location)];
NSString *right = [formula substringFromIndex:rRange.location + 1];
// 括号内的表达式
NSString *middle = [formula substringWithRange:NSMakeRange(lRange.location+1, rRange.location-lRange.location-1)];
// 代入计算新的公式
NSString *newFormula = [NSString stringWithFormat:@"%@%@%@", left, [self calcNormalFormula:middle], right];
return [self calcComplexFormulaString:newFormula];
}

@end

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

posted @ 2013-12-03 22:18  Kurodo  阅读(5144)  评论(0编辑  收藏  举报