iOS:Case.计算器Calculator Modal写法对比
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============自己的============
定义:
double result; NSString *operator; NSMutableString *operand1; double operand0;主要方法:
// 获取结果-(NSString *)getCalculateOutput{ return [NSString stringWithFormat:@"%f",result];}//处理输入-(void)dealWithInput:(NSString *)input{ // num if ([self inputIsOperand:input]) { [operand1 appendString:input]; result = [operand1 doubleValue]; }else{ // operator int whichOperator = [self getOperator:operator]; switch (whichOperator) { case 0: result = [operand1 doubleValue]; break; case 1: result = [operand1 doubleValue] + operand0; break; case 2: result = [operand1 doubleValue] - operand0; break; case 3: result = [operand1 doubleValue] * operand0; break; case 4: result = [operand1 doubleValue] / operand0; break; default: break; } operand0 = result; operator = [NSString stringWithString:input]; [operand1 setString:@""]; }}-(BOOL)inputIsOperand:(NSString *)input{ if ([@"0123456789" rangeOfString:input].length > 0) { return YES; } return NO;}-(int)getOperator:(NSString *)aOperator{ if ([aOperator isEqualToString:@"+"]) { return Add; }else if([aOperator isEqualToString:@"-"]){ return Sub; }else if([aOperator isEqualToString:@"*"]){ return Mul; }else if([aOperator isEqualToString:@"*"]){ return Div; } return non;}
============官网============
定义:
@private NSMutableString *_display; // The calculator display (the value a harwdare-based calculator shows on its LCD screen). double _operand; NSString *_operator;
// These string constants contain the characters that the input: method accepts.const NSString *Operators = @"+-*/";const NSString *Equals = @"=";const NSString *Digits = @"0123456789.";const NSString *Period = @".";const NSString *Delete = @"D";const NSString *Clear = @"C";主要方法:
/* * The input: method accepts the characters in the string constants * Operators, Equals, Digits, Period Delete, and Clear. * * The results of this method's computations are stored in _display. * This method uses _operand, and _operator in its calculations. */- (void) input:(NSString *) input_character { static BOOL last_character_is_operator = NO; BOOL bad_character; // Does input_character contain exactly one character? if (!(bad_character = !(input_character && [input_character length] == 1))) { // Is input_character in Digits? if ([Digits rangeOfString: input_character].length) { if (last_character_is_operator) { // Set the display to input_character. [_display setString: input_character]; last_character_is_operator = NO; } // Is input_character a digit, or is a period while a period has not been added to _display? else if (![input_character isEqualToString: (NSString *)Period] || [_display rangeOfString: (NSString *)Period].location == NSNotFound) { // Add input_character to _display. [_display appendString:input_character]; } } // Is input_character in Operators or is it Equals? else if ([Operators rangeOfString:input_character].length || [input_character isEqualToString:(NSString *)Equals]) { if (!_operator && ![input_character isEqualToString:(NSString *)Equals]) { // input_character is this calculation's operator. // // Save the operand and the operator. _operand = [[self displayValue] doubleValue]; _operator = input_character; } else { // input_character is in Operators or Equals. // // Perform the computation indicated by the saved operator between the saved operand and _display. // Place the result in _display. if (_operator) { double operand2 = [[self displayValue] doubleValue]; switch ([Operators rangeOfString: _operator].location) { case 0: _operand = _operand + operand2; break; case 1: _operand = _operand - operand2; break; case 2: _operand = _operand * operand2; break; case 3: _operand = _operand / operand2; break; } [_display setString: [[NSNumber numberWithDouble: _operand] stringValue]]; } // Save the operation (if this is a chained computation). _operator = ([input_character isEqualToString:(NSString *)Equals])? nil : input_character; } last_character_is_operator = YES; } // Is input_character Delete? else if ([input_character isEqualToString:(NSString *)Delete]) { // Remove the rightmost character from _display. NSInteger index_of_char_to_remove = [_display length] - 1; if (index_of_char_to_remove >= 0) { [_display deleteCharactersInRange:NSMakeRange(index_of_char_to_remove, 1)]; last_character_is_operator = NO; } } // Is input_character Clear? else if ([input_character isEqualToString:(NSString *)Clear]) { // If there's something in _display, clear it. if ([_display length]) { [_display setString:[NSString string]]; } // Otherwise, clear the saved operator. else { _operator = nil; } } else { // input_character is an unexpected (invalid) character. bad_character = TRUE; } } if (bad_character) { // Raise exception for unexpected character. NSException *exception = [NSException exceptionWithName:NSInvalidArgumentException reason:@"The input_character parameter contains an unexpected value." userInfo:[NSDictionary dictionaryWithObjectsAndKeys: input_character, @"arg0", nil]]; [exception raise]; }}#pragma mark Outlets/* * The displayValue method rerutns a copy of _display. */- (NSString *) displayValue { if ([_display length]) { return [_display copy]; } return @"0";}
###############对比###############
---------算法-----------
--变量:
result:存储当前要显示的结果
operand0:存储上一个操作数
operator:存储上一个操作符
operand1:存储当前操作数
--输入处理:
输入如果是数字,保存为operand1,更新result的值;如果是操作符,则将之前保存的operand0、operator和operand1计算,并将结果保存为新的operand0,当前操作符保存为operator;更新result的值;
--输出:
显示result的值
---------------
--变量:
_display:显示的结果(当前操作数)
_operand:存储上一个操作数
_operator:存储上一个操作数
--输入处理:
输入如果是数字,_display接收输入,更新_display; 输入如果是运算符,判断是不是第一个运算符号,{如果是,保持操作数_operand和当前操作符_operator} {如果不是,将当前操作数_display、之前操作数_operand、操作符_operator运算,结果保存为新的operand,当前操作符保存为operator} 更新_display;
--输出思路:
显示_display的值
-------比较
-大体一样,不过例2更精简(直接用显示的_display代替operand1,虽然_display显示的时候不总代表当前操作数operand1,但只要是开始运算,_display完全就是当前operand1),更全面(首个运算符号的判断);而且这更符合计算器model的思路,随意的输入值然后从display中get结果。
-算法,不仅仅要考虑变量选择,逻辑思路,对于变量初值的选择也很重要,_display为空字符串,operator为nil,lastCharacterIsOperator为no,这些值跟算法思路和逻辑分支判断完全对起来了;这些初值完全适用代码的逻辑判断,
-一个算法最基本要满足‘正常情况/循环结构’的处理,好的算法,变量初值完全契合‘正常情况/循环结构’,就像该例,循环结构为:碰到数字,更新显示;碰到运算符,如果运算符为nil怎么处理,或者用operator运算当前显示和operand,或者更新运算符(本例子不是做更新处理,另外一种思路);这些情况初值完全适用,开始时候,输入数字,更新display,如果输入计算符,默认operand为0,同时operator为当前输入的运算符。算法思路详见‘算法’分类中‘概念’文章。
----------命名问题----------
--result既然是存储着要显示的结果,叫display更合理;它不是运算结果(当输入操作数的时候,它的值为操作数)
--成员变量名字没有前缀下划线;
----------质量问题----------
--没有异常判断:对输入的字符串长度是不是1,有没有值,没判断,直接当作正确的去用了;
--没有合法值判断:输入的字符串应该限定在自己接受的范围内;
--考虑条件不够全面,算法逻辑不清晰:当运算完,当前操作符为‘=’号和其它符号的区别处理
----------其他技巧----------
- 第一个操作数为double类型,操作符和第二个操作数位字符串类型;
- 输入一个字符串判断是哪个字符:switch方法([const字符串常量 rangOfString ].location),其中case直接是数字,而不用写很多if,else if判断;
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