第 4 節

operator

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operator

Function: For performing code computations

In this chapter, we will mainly cover the following types of operators:

Operator Types	Purpose
arithmetic operators	for processing four arithmetic operations
Assignment operator	Assigns the value of an expression to a variable
Comparison Operators	Used for comparing expressions and returning a true or false value.
Logical operators	Used to return a true or false value based on the result of an expression.

arithmetic operators

Purpose: Used to handle arithmetic operations

Arithmetic operators include the following symbols:

Operator	Terminology	Example	Results
+	Plus sign	+3	3
-	minus sign	-3	-3
+	add	10 + 5	15
-	subtract	10 - 5	5
*	multiply	10 * 5	50
/	remove	10 / 5	2
%	modulo (remainder)	10 % 3	1
++	pre-increment	a=2; b=++a;	a=3; b=3;
++	Post-increment	a=2; b=a++;	a=3; b=2;
--	pre-decrement	a=2; b=--a;	a=1; b=1;
--	post-decrement	a=2; b=a--;	a=1; b=2;

Example 1:

//加减乘除
int main() {

    int a1 = 10;
    int b1 = 3;

    cout << a1 + b1 << endl;
    cout << a1 - b1 << endl;
    cout << a1 * b1 << endl;
    cout << a1 / b1 << endl;  //两个整数相除结果依然是整数

    int a2 = 10;
    int b2 = 20;
    cout << a2 / b2 << endl; 

    int a3 = 10;
    int b3 = 0;
    //cout << a3 / b3 << endl; //报错，除数不可以为0

    //两个小数可以相除
    double d1 = 0.5;
    double d2 = 0.25;
    cout << d1 / d2 << endl;


    return 0;
}

Running/Observation Results: After running, the corresponding content will be printed according to the output statements. The variable values can be inferred based on the order of initialization, assignment, and function calls.

Summary: In division operations, the divisor cannot be zero.

Example 2:

//取模
int main() {

    int a1 = 10;
    int b1 = 3;

    cout << 10 % 3 << endl;

    int a2 = 10;
    int b2 = 20;

    cout << a2 % b2 << endl;

    int a3 = 10;
    int b3 = 0;

    //cout << a3 % b3 << endl; //取模运算时，除数也不能为0

    //两个小数不可以取模
    double d1 = 3.14;
    double d2 = 1.1;

    //cout << d1 % d2 << endl;


    return 0;
}

Summary: Only integer variables can perform modulo operations.

Example 3:

//递增
int main() {

    //后置递增
    int a = 10;
    a++; //等价于a = a + 1
    cout << a << endl; // 11

    //前置递增
    int b = 10;
    ++b;
    cout << b << endl; // 11

    //区别
    //前置递增先对变量进行++，再计算表达式
    int a2 = 10;
    int b2 = ++a2 * 10;
    cout << b2 << endl;

    //后置递增先计算表达式，后对变量进行++
    int a3 = 10;
    int b3 = a3++ * 10;
    cout << b3 << endl;


    return 0;
}

Summary: Prefix increment applies ++ to the variable first before evaluating the expression, while postfix increment does the opposite.

Assignment operator

Function: Used to assign the value of an expression to a variable

赋值运算符包括以下几个符号：=、+=、-=、*=、/=、%=。

Operator	Terminology	Example	Results
=	assign value	a=2; b=3;	a=2; b=3;
+=	plus equals	a=0; a+=2;	a=2;
-=	minus equals	a=5; a-=3;	a=2;
*=	Multiply equals	a=2; a*=2;	a=4;
/=	division equals	a=4; a/=2;	a=2;
%=	Modulo equals	a=3; a%2;	a=1;

Example:

int main() {

    //赋值运算符

    // =
    int a = 10;
    a = 100;
    cout << "a = " << a << endl;

    // +=
    a = 10;
    a += 2; // a = a + 2;
    cout << "a = " << a << endl;

    // -=
    a = 10;
    a -= 2; // a = a - 2
    cout << "a = " << a << endl;

    // *=
    a = 10;
    a *= 2; // a = a * 2
    cout << "a = " << a << endl;

    // /=
    a = 10;
    a /= 2;  // a = a / 2;
    cout << "a = " << a << endl;

    // %=
    a = 10;
    a %= 2;  // a = a % 2;
    cout << "a = " << a << endl;


    return 0;
}

Comparison Operators

Purpose: Used for comparing expressions and returning a true or false value.

Comparison operators use the following symbols:

Operator	Terminology	Example	Results
==	equivalent to	4 == 3	0
!=	not equal to	4 != 3	1
<	less than	4 < 3	0
>	greater than	4 > 3	1
<=	less than or equal to	4 <= 3	0
>=	greater than or equal to	4 >= 1	1

Example:

int main() {

    int a = 10;
    int b = 20;

    cout << (a == b) << endl; // 0 

    cout << (a != b) << endl; // 1

    cout << (a > b) << endl; // 0

    cout << (a < b) << endl; // 1

    cout << (a >= b) << endl; // 0

    cout << (a <= b) << endl; // 1
    

    return 0;
}

Note: In comparison operations for C and C++ languages, "true" is represented by the number "1," and "false" is represented by the number "0."

Logical operators

Purpose: Returns true or false based on the value of an expression.

Logical operators have the following symbols:

Operator	Terminology	Example	Results
!	Non-	!a	If a is false, then !a is true; if a is true, then !a is false.
&&	and	a && b	If both a and b are true, the result is true; otherwise, it is false.
\|\|	or	a \|\|b	If either a or b is true, the result is true; if both are false, the result is false.

Example 1: Logical NOT

//逻辑运算符  --- 非
int main() {

    int a = 10;

    cout << !a << endl; // 0

    cout << !!a << endl; // 1


    return 0;
}

Summary: What is real becomes fake, and what is fake becomes real.

Example 2: Logic AND

//逻辑运算符  --- 与
int main() {

    int a = 10;
    int b = 10;

    cout << (a && b) << endl;// 1

    a = 10;
    b = 0;

    cout << (a && b) << endl;// 0 

    a = 0;
    b = 0;

    cout << (a && b) << endl;// 0


    return 0;
}

Summary: Summary of the logical ==AND== operator: True only when both sides are true, otherwise false.

Example 3: logical OR

//逻辑运算符  --- 或
int main() {

    int a = 10;
    int b = 10;

    cout << (a || b) << endl;// 1

    a = 10;
    b = 0;

    cout << (a || b) << endl;// 1 

    a = 0;
    b = 0;

    cout << (a || b) << endl;// 0


    return 0;
}

Logical ==OR== operator summary: ==False only when both are false, true otherwise==