operators - sluczak/cpp_by_example GitHub Wiki

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Operators

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Examples for this part available on git after calling the command:

git checkout -b origin operators

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What are operators used for?

Operators are used to interact with the variables in order to assure the proper application flow and/or change value of variables. There are:

• arithmetic,
• logical,
• relation and
• other operators.

Arithmetic operators

Two-variable operators

Arithmetic operators are mostly the two-variable operators. They represent the arithmetic operations on variables.

Arithmetic operations may be organized with use of parenthesis ( and ). Code below shows the usage of such operators:

   int a = 2 - 1;       // subtraction
   int b = a + 6;       // addition
   int c = a * (b + 1); // multiplication with nested operation 
   int d = c / 1;       // division

One-variable operators

The simpliest one-variable operator available in C++ is a negation of value; c++ int i = 2; int b = -i; // b = -2

C++ has also some arithmetic one-argument operators, which are used to easily increment or decrement integer value.

++i is a pre-increment operator. Value of i will be incremented before accessing the variable

i++ is a post-increment operator. Value of i will be incremented, but the current access to the variable will return the value before incrementation.

and analogously --i pre-decrement and i-- post-decrement.

The subtle difference between pre and post operations are shown in the source code below:

int a = 5;
int b = ++a; // a = 6; b = 6; - pre-incrementation

int c = 5;
int d = c++; // c = 6; d = 5; - post-incrementation

The post-incrementation operator might be a little bit confusing, because:

First, d will be assigned value of c before incrementation, so d = 5;

Second, c will be incremented, so c = 6;

Operation with assignment

There is also third type of arithmetic operators, which combine the arithmetic operation on variable and the instant assignment of the result value: +=, -=, *=, /=.

Those operators and its results are shown in the source code below:

 int a = 5;
 int b = 3;
 a += 3;    // "add 3 to a and assign result to a"        a = 5 + 3 = 8;
 a *= b;    // "multiply a by b and assign to a"          a = 8 * 3 = 24;
 a /= b;    // "divide a by b and assign to a"            a = 24 / 3 = 8;
 b -= 1;    // sybstract 1 from b and assign result to b" b = 3 - 1 = 2;

Relation operators

In order to control the operations flow, c++ has the common relation operators. Their result is always a value of boolean logic: true or false. Here are listed all the relation operators available:

a < b - if a value is lower than b, then return true. Else return false

a > b - if a value is greater than b, then return true. Else return false

a <= b - if a value is lower than, or equal to b, then return true. Else return false

a >= b - if a value is greater than, or equal to b, then return true. Else result false

While operators above doesn't work with logical bool variables, operators below can be used for both: numerical and boolean values.

a == b - if a value is not equal to b, then return true. Else return false

a != b - if a value is not equal to b, then return true. Else return false

The relational operators are useful in flow control instructions:

int a = 2;
int b = 3;
bool isBusy = false;

if(a > b) {
   //do something
}

if(a != b) {
   //do something else
}

if(isBusy == false) {
   //rest
}

Logical operators

Logical operators are used to perform operations on boolean-only variables and values. The logical negation operator - ! exclamation mark is used to invert the value of variable.

   bool isBusy = true;
   if(!isBusy) { //if is not busy
       //rest
   }

   bool logicalValue = true;
   bool negationOfLogicalValue = !logicalValue; // negationOfLogicalValue = false;

In case of situations, where several conditions has to be met simultaneously, programmer may use the two-variable operators listed below:

&& - logical AND

|| - logical OR

conditionA && conditionB returntrue only if conditionA and conditionB are true

conditionA || conditionB return true if both: conditionA and conditionB are true or conditionA is true or conditionB is true

Other operators

C++ has also a three-argument conditional operator:

condition ? doInResultForTrue : doInResultForFalse;

if-condition will be covered in flow control topic

This operator is a shortened version of if-condition, but because of low readability, I suggest to use normal if-condition instead of it.

There are also bitwise operators and stream operators, but we won't cover them in here.

stream operators will be shown with streams topic

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