4.6: Assignment Operator

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Assignment Operator

The assignment operator allows us to change the value of a modifiable data object (for beginning programmers this typically means a variable). It is associated with the concept of moving a value into the storage location (again usually a variable). Within C++ programming language the symbol used is the equal symbol. But bite your tongue, when you see the = symbol you need to start thinking: assignment. The assignment operator has two operands. The one to the left of the operator is usually an identifier name for a variable. The one to the right of the operator is a value.

Simple Assignment

int    age;    // variable set up
// then later in the program
age = 21;

The value 21 is moved to the memory location for the variable named: age. Another way to say it: age is assigned the value 21.

Assignment with an Expression

int total_cousins;    // variable set up
// then late in the program
total_cousins = 4 + 3 + 5 + 2;

The item to the right of the assignment operator is an expression. The expression will be evaluated and the answer is 14. The value 14 would assigned to the variable named: total_cousins.

Assignment with Identifier Names in the Expression

int    students_period_1 = 25;    // variable set up with initialization
int    students_period_2 = 19;
int    total_students;
// then late in the program
total_students = students_period_1 + students_period_2;

The expression to the right of the assignment operator contains some identifier names. The program would fetch the values stored in those variables; add them together and get a value of 44; then assign the 44 to the total_students variable.

As we have seen, assignment operators are used to assigning value to a variable. The left side operand of the assignment operator is a variable and right side operand of the assignment operator is a value. The value on the right side must be of the same data-type of the variable on the left side otherwise the compiler will raise an error.
Different types of assignment operators are shown below:

“=”: This is the simplest assignment operator, which was discussed above. This operator is used to assign the value on the right to the variable on the left.
For example:
```
a = 10;
b = 20;
ch = 'y';
```
+=: This operator is combination of ‘+’ and ‘=’ operators. This operator first adds the current value of the variable on left to the value on the right and then assigns the result to the variable on the left.
Example:
```
(a += b) can be written as (a = a + b)
```
If initially the value 5 is stored in the variable a, then: (a += 6) is equal to 11. (the same as: a = a + 6)
-= This operator is combination of ‘-‘ and ‘=’ operators. This operator first subtracts the current value of the variable on left from the value on the right and then assigns the result to the variable on the left.
Example:
```
(a -= b) can be written as (a = a - b)
```
If initially value 8 is stored in the variable a, then (a -= 6) is equal to 2. (the same as a = a - 6)
*= This operator is combination of ‘*’ and ‘=’ operators. This operator first multiplies the current value of the variable on left to the value on the right and then assigns the result to the variable on the left.
Example:
```
(a *= b) can be written as (a = a * b)
```
If initially value 5 is stored in the variable a,, then (a *= 6) is equal to 30. (the same as a = a * 6)
/= This operator is combination of ‘/’ and ‘=’ operators. This operator first divides the current value of the variable on left by the value on the right and then assigns the result to the variable on the left.
Example:
```
(a /= b) can be written as (a = a / b)
```
If initially value 6 is stored in the variable a, then (a /= 2) is equal to 3. (the same as a = a / 2)

Below example illustrates the various Assignment Operators:

// C++ program to demonstrate 
// working of Assignment operators 
#include <iostream>
using namespace std;
  
int main() 
{ 
    // Assigning value 10 to a 
    // using "=" operator 
    int a = 10; 
    cout << "Value of a is "<< a <<"\n"; 
  
    // Assigning value by adding 10 to a 
    // using "+=" operator 
    a += 10; 
    cout << "Value of a is "<< a <<"\n"; 
  
    // Assigning value by subtracting 10 from a 
    // using "-=" operator 
    a -= 10; 
    cout << "Value of a is "<< a <<"\n"; 
  
    // Assigning value by multiplying 10 to a 
    // using "*=" operator 
    a *= 10; 
    cout << "Value of a is "<< a <<"\n"; 
  
    // Assigning value by dividing 10 from a 
    // using "/=" operator 
    a /= 10; 
    cout << "Value of a is "<< a <<"\n"; 
  
    return 0; 
}

Output:

Value of a is 10
Value of a is 20
Value of a is 10
Value of a is 100
Value of a is 10

Definitions

assignment: An operator that changes the value of a modifiable data object.

Adapted from: "Assignment Operator" by Kenneth Leroy Busbee, (Download for free at http://cnx.org/contents/303800f3-07f...93e8948c5@22.2) is licensed under CC BY 4.0