Objective-C > Operating Expression

• Expression has precedence (優先次序).
• Expression syntax:

operand1;  operand1 operator operand2;  operand1? operand2: operand3;

• Basic expression: +a, -a, a++/++a, a--/--a, ~a()

int a = -3;                                             int b = +a;               // b = + (-3) = -3  int c = -a;               // c = -(-3) = 3

int a = 3;  int b = ++a;              // b = 3 + 1 = 4  int c = a++;              // c = a = 3  int d = --a;              // d = 3 - 1 = 2  int e = a--;              // e = a = 3

BOOL a = YES;  BOOL b = !a;              // b = NO  BOOL c = !b;              // c = YES

• Arithmetic operators: + , - , * , / , % (for 取餘數)
• a

int a = 11;  int b = a + 33;           // b = 11 + 33 = 44  int c = b - 22;           // c = 44 - 22 = 22  int d = c *11;            // d = 22 x 11 = 242  int e = d / 44;           // e = 242 / 44 = 5  int f = e % 55;           // f = 5 %55 = 5

• Equity and relational operators: == , != , > , >= , < , <=

int a = 11;  int b = 22;  BOOL c = a >= b;          // c = NO since c = 11 >= 22  BOOL d = a <= b;          // d = YES since d = 11 <= 22  BOOL e = c == d;          // e = NO since c = NO is not equal to d = YES  BOOL f = a != b;          // f YES since a = 11 is not equal to b = 22  BOOL f = (a != b);        // same as the above

• Equal symbols: = , += , -= , /= , %= , <=

int a = 11;  a += 33;                  // a = a + 33 = 11 + 33 = 44  a -= 22;                  // a = a - 22 = 44 - 22 = 22  a *= 11;                  // a = a * 11 = 22 * 11 = 242  a /= 44;                  // a = a / 44 = 242 / 44 = 5  a %= 55;                  // a = a % 55 = 5 % 55 = 5

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<<Comma Operator (,)>>

• Allows you to use two or more expressions where only one is expected
• It evaluates the first operand (usually an expression), then discards the results
• Then it evaluates the second operand and return the value

a = (b = 3,  b  + 2)