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一、实现思路

先搭建好MVC框架，接着在各个模块中实现各自的任务。首先要创建好UI界面，接着根据UI界面的元素来与数据进行互动，其中创建UI界面需要用到Masonry布局。

二、实现方法

在calculationView文件中只涉及到UI界面。
首先创建两个UITextField对象，一个用来显示输入到表达式，一个用来输出运算结果，接着创建一个数组用来存放button的名称，接着循环创建button对象即可。

创建button时需要设置button的tag属性，因为后面需要通过button的tag属性来进行逻辑判断。

self.textField01 = [[UITextField alloc] init];
self.textField01.backgroundColor = [UIColor blackColor];
self.textField02 = [[UITextField alloc] init];
self.textField02.backgroundColor = [UIColor blackColor];
self.buttonArray = [NSMutableArray arrayWithObjects:@"AC", @"(", @")", @"/", @"1", @"2", @"3", @"+", @"4", @"5", @"6", @"-", @"7", @"8", @"9", @"*",  @"0", @".", @"=", nil];for (int i = 0; i < 4; i++) {for (int j = 0; j < 4; j++) {self.calculatorButton = [UIButton buttonWithType:UIButtonTypeCustom];NSString* buttonString = self.buttonArray[i * 4 + j];[self.calculatorButton setTitle:buttonString forState:UIControlStateNormal];self.calculatorButton.titleLabel.font = [UIFont systemFontOfSize:43];self.calculatorButton.titleLabel.textColor = [UIColor whiteColor];self.calculatorButton.backgroundColor = [UIColor grayColor];[self.calculatorButton addTarget:self action:@selector(pressButton:) forControlEvents:UIControlEventTouchUpInside];self.calculatorButton.layer.borderWidth = 2.0;self.calculatorButton.layer.cornerRadius = ButtonSize / 2;self.calculatorButton.layer.masksToBounds = YES;self.calculatorButton.tag = 100 + j + i*4;if (i == 0 && j < 3) {self.calculatorButton.backgroundColor = [UIColor colorWithWhite:0.6 alpha:0.9];self.calculatorButton.titleLabel.textColor = [UIColor blackColor];}if (j == 3) {self.calculatorButton.backgroundColor = [UIColor orangeColor];}[self addSubview:self.calculatorButton];[self.calculatorButton mas_makeConstraints:^(MASConstraintMaker *make) {make.top.equalTo(self).offset(90 + HEIGHT / 6 + HEIGHT / 8 + (ButtonSize + SideSize) * i);make.left.equalTo(self).offset(SideSize + (ButtonSize + SideSize) * j);make.width.equalTo(@ButtonSize);make.height.equalTo(@ButtonSize);}];}}

还需要在当前文件触发button的事件函数，因为要通过button的事件函数将当前button传值到CalculationViewController文件中。

我使用的协议传值进行

定义协议及协议方法

@protocol ButttonDelegate <NSObject>- (void)returnButton:(UIButton*)button;@end

定义代理对象

@property (nonatomic, weak)id<ButttonDelegate>delegate;

button事件函数触发代理方法

- (void)pressButton:(UIButton*)button {[self.delegate returnButton:button];
}

在CalculationViewController中定义协议方法

- (void)returnButton:(UIButton*)button;

在CalculationViewController中设置代理对象

 self.calculationView.delegate = self;

在CalculationViewController中实现协议方法

- (void)returnButton:(UIButton*)button {
- NSString* buttonStr = button.titleLabel.text;NSInteger buttonTag = button.tag;if (buttonTag == 100) {self.calculationView.textField01.text = @"";self.calculationView.textField02.text = @"";self.yunsuanStr = [[NSMutableString alloc] init];self.jieguoStr = [[NSString alloc] init];} else if (buttonTag == 118) {//四则运算}//
}

对于四则运算，我使用中缀表达式转后缀表达式，再利用后缀表达式进行计算。中缀转后缀定义一个符号栈，一个结果栈。

		char resultStack[100];int resultTop = -1;char operationStack[100];int operationTop = -1;NSString* ocStr =  self.yunsuanStr;const char* strs = [ocStr UTF8String];char str[1000] ;strcpy(str, strs) ;int length = (int)strlen(str);

后缀进行四则运算时定义一个新栈。

			double Stack[100];int StackTop = -1;char* token = strtok(resultStack, " ");while (token != NULL) {if (strcmp(token, "+") == 0) {double a = Stack[StackTop--];double b = Stack[StackTop--];double c = b + a;Stack[++StackTop] = c;}else if (strcmp(token, "-") == 0) {double a = Stack[StackTop--];double b = Stack[StackTop--];double c = b - a;Stack[++StackTop] = c;}else if (strcmp(token, "*") == 0) {double a = Stack[StackTop--];double b = Stack[StackTop--];double c = b * a;Stack[++StackTop] = c;}else if (strcmp(token, "/") == 0) {double a = Stack[StackTop--];double b = Stack[StackTop--];double c = b / a;Stack[++StackTop] = c;}else if (strcmp(token, "!") == 0) {double c = Stack[StackTop--];c = -c;Stack[++StackTop] = c;}else {double num = atof(token);Stack[++StackTop] = num;}token = strtok(NULL, " ");}double result = Stack[StackTop--];

这里使用了atof()函数可以将字符串中的数字识别为double类型的浮点数。使用strtok()函数将结果栈的元素通过空格分割方便进行识别和运算。

对于负数的运算，我是将与“（”相邻的“-”转换为“！”，并用“！”进行负数转变，其中需要将“！“的优先级设置为最高

int Compare(char str) {if (str == '(' || str == ')') {return 0;}else if (str == '+' || str == '-') {return 1;}else if (str == '*' || str == '/') {return 2;} else if (str == '!') {return 3;} else {return -1;}
}

接着在输入字符串时进行识别

for (int i = 0; i < length; ++i) {if (str[i] == '(' && str[i + 1] == '-') {str[i + 1] = '!';}}

三、判错处理

对于括号匹配问题，我使用栈来处理，当读到“（”则入栈，读到“）”则栈顶元素出栈，最后判断栈是否为空即可。

- (int)kuoHaoMatch:(NSMutableString*)mutableString {const char* cstr = [mutableString UTF8String];int length = (int)strlen(cstr);char stack[100];int stackTop = -1;for (int i = 0; i < length; i++) {if (cstr[i] == '(') {stack[++stackTop] = cstr[i];}if (cstr[i] == ')') {stack[stackTop--];}}if (stackTop == -1) {return 1;}return 0;
}

对于符号匹配问题，两个运算符不能相邻，第一个位置不能为运算符（-除外），最后一个位置不能为运算符

- (int)fuHaoMatch:(NSMutableString*)mutableString {const char* cstr = [mutableString UTF8String];int length = (int)strlen(cstr);if (cstr[0] == '*' || cstr[0] == '/' || cstr[0] == '+') {return 0;}for (int i = 0; i < length; i++) {if ((cstr[i] == '*' && cstr[i+1] == '/') || (cstr[i] == '/' && cstr[i+1] == '*')) {return 0;}if ((cstr[i] == '*' && cstr[i+1] == '-') || (cstr[i] == '*' && cstr[i+1] == '+')) {return 0;}if ((cstr[i] == '/' && cstr[i+1] == '-') || (cstr[i] == '/' && cstr[i+1] == '+')) {return 0;}if ((cstr[i] == '+' && cstr[i+1] == '/') || (cstr[i] == '+' && cstr[i+1] == '*')) {return 0;}if ((cstr[i] == '-' && cstr[i+1] == '/') || (cstr[i] == '-' && cstr[i+1] == '*')) {return 0;}if ((cstr[i] == '-' && cstr[i+1] == '-') || (cstr[i] == '-' && cstr[i+1] == '+')) {return 0;}if ((cstr[i] == '+' && cstr[i+1] == '+') || (cstr[i] == '+' && cstr[i+1] == '-')) {return 0;}}if (cstr[length - 1] == '+' || cstr[length - 1] == '-' ||cstr[length - 1] == '*' || cstr[length - 1] == '/') {return 0;}return 1;
}

对于数字和括号的相邻问题，数字后不能直接跟左括号，右括号不能直接跟数字

- (int)numberAndkuoHao:(NSMutableString*)mutableString {const char* cstr = [mutableString UTF8String];int length = (int)strlen(cstr);int flag = 0;for (int i = 0; i < length; i++) {if ((cstr[i]>= '0' && cstr[i] <= '9') &&cstr[i+1] == '(') {flag++;}if (cstr[i] == ')' && (cstr[i + 1]>= '0' && cstr[i + 1] <= '9')) {flag++;}}if (flag == 0) {return 1;}return 0;
}

对于只有括号没有数字的问题，直接遍历整个字符串如果有数字则标志变量加一，最后判断标志变量

- (int)numberJudge:(NSMutableString*)mutableString {const char* cstr = [mutableString UTF8String];int length = (int)strlen(cstr);int flag = 0;for (int i = 0; i < length; i++) {if (cstr[i]>= '0' && cstr[i] <= '9') {flag++;}}if (flag != 0) {return 1;}return 0;;
}

对于除零问题

if ([self.jieguoStr isEqualToString:@"nan"]) {self.jieguoStr = @"错误";}if ([self.jieguoStr isEqualToString:@"inf"]) {self.jieguoStr = @"错误";}

对于小数点异常处理

int pointFlag = 0;
for (int i = 0; i < resultTop; i++) {if (resultStack[i] == '.') {for (int j = i + 1; resultStack[j] != ' '; j++) {if (resultStack[j] == '.') {pointFlag++;}}}}if (pointFlag != 0) {self.jieguoStr = @"错误";pointFlag = 0;}

对于如何删除多余的零

NSDecimalNumber *number = [NSDecimalNumber decimalNumberWithString: self.jieguoStr];NSDecimalNumberHandler *roundHandler = [NSDecimalNumberHandler decimalNumberHandlerWithRoundingMode:NSRoundUp scale:8 raiseOnExactness:NO raiseOnOverflow:NO raiseOnUnderflow:NO raiseOnDivideByZero:NO];NSDecimalNumber *roundedNumber = [number decimalNumberByRoundingAccordingToBehavior:roundHandler];self.jieguoStr = [roundedNumber stringValue];