2.2 Completing the basics

Assignment operators

Assignment operator (=) is used for assignment a value to a variable and for performing computations.

Assignment statement has the syntax:

variable = expression;

Expression is any combination of constants, variables, and function calls that can be evaluated to yield a result.

Example:

length = 25;

cMyCar = “Mercedes”;

sum = 3 + 7;

newtotal = 18.3*amount;

slope = (y2 – y1)/(x2 – x1);

The order of events when the computer executes an assignment statement is

- Evaluate the expression on the right hand side of the assignment operator.

- Store the resultant value of the expression in the variable on the left hand side of the assignment operator.

Note:

1. It’s important to note that the equal sign in C++ does not have the same meaning as an equal sign in mathematics.

2. Each time a new value is stored in a variable, the old one is overwritten.

Example

// This program calculates the volume of a cylinder,

// given its radius and height

#include<iostream.h>

int main()

{

float radius, height, volume;

radius = 2.5;

height = 16.0;

volume = 3.1416 * radius * radius * height;

cout<<"The volume of the cylinder is "<<volume<<endl;

return 0;

}

The output of the above program:

The volume of the cylinder is 314.16

We can write multiple assignments , such as a = b = c = 25;. Because the assignment operator has a right-to-left associativity, the final evaluation proceeds in the sequence

c = 25;

b = 25;

c = 25;

Data type conversion across assignment operator

Note that data type conversion can take place across assignment operators, that is, the value of the expression on the right side of the assignment operator is converted to the data type of the variable to the left side of the assignment operator.

For example, if temp is an integer variable, the assignment temp = 25.89 causes the integer value 25 to be stored in the integer variable temp.

Assignment variations

C++ also use a shorthand notation to perform an operation and an assignment at the same time. This is denoted by an operator followed by an equal sign. For example, to add 4 to the variable x and assign x to the result, you say: x += 4. Figure 1 illustrates assignment operator and all assignment variations.

Assignment statements such as sum += 10 or its equivalent, sum = sum + 10, are very common in C++ programming.

Increment and decrement operators

For the special case in which a variable is either increased or decreased by 1, C++ provides two unary operators: increment operator and decrement operator .

The increment (++) and decrement (--) unary operators can be used as prefix or postfix operators to increase or decrease value.

A prefix operator is placed before a variable and returns the value of the operand after the operation is performed.