03 1 Operators And Expressions

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Chapter 3:Operators and Expressions| SCP1103 Programming Technique C | Jumail, FSKSM, UTM, 2006 |Last Updated: July 2006 Slide 1

Operators and Expressions

Lecture 3

byJumail Bin Taliba

Faculty of Computer Science & Information System

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Elements of a program

Literals fixed data written into a program Variables & constants placeholders (in

memory) for pieces of data Types sets of possible values for data Expressions combinations of operands (such

as variables or even "smaller" expressions) and operators. They compute new values from old ones.

Assignments used to store values into variables Statements "instructions". In C, any expression

followed by a semicolon is a statement

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Elements of a program

Control-flow constructs constructs that allow statements or groups of statements to be executed only when certain conditions hold or to be executed more than once.

Functions named blocks of statements that perform a well-defined operation.

Libraries collections of functions.

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Statement

Statements are elements in a program which (usually) ended up with semi-colon (;) e.g. below is a variables declaration statement

int a, b, c;

• Preprocessor directives (i.e. #include and define) are not statements. They don’t use semi-colon

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Some types of statement in C++

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An expression statement is a statement that results a value

Some examples of expression Value

• Literal expression e.g. 2, “A+”, ‘B’

The literal itself

• Variable expression e.g. Variable1

• arithmetic expression e.g. 2 + 3 -1

The content of the variable

The result of the operation

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Operators

Operators can be classified according to the type of their operands and of their output

Arithmetic Relational Logical Bitwise

the number of their operands Unary (one operand) Binary (two operands)

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Binary expression

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Unary Expression

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Ternary Expression

(a>2) ? 1: 0

Operator

First operand is a condition

Second operand is a value

Third operand is another value

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Arithmetic operators

They operate on numbers and the result is a number.

The type of the result depends on the types of the operands.

If the types of the operands differ (e.g. an integer added to a floating point number), one is "promoted" to other.

The "smaller" type is promoted to the "larger" one.

char int float double

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Example of promotion:The result of the following “double division” is 2.5

5 / 2.0

Before the division process, 5 is promoted from integer 5 to float 5.0

The result of the following “integer division” is 25 / 2

There is no promotion occurred. Both operands are the same type.

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Arithmetic operators: +, *

+ is the addition operator * is the multiplication operator They are both binary

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Arithmetic operator:

This operator has two meanings: subtraction operator (binary)

negation operator (unary)

e.g. 31 - 2

e.g. -10

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Arithmetic operator: /

Division operator CAREFUL! The result of integer division is an integer:

e.g. 5 / 2 is 2, not 2.5

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Arithmetic operator: %

The modulus (remainder) operator. It computes the remainder after the first

operand is divided by the second

It is useful for making cycles of numbers: For an int variable x :

if x is: 0 1 2 3 4 5 6 7 8 9 ...(x%4) is: 0 1 2 3 0 1 2 3 0 1 ...

e.g. 5 % 2 is 1, 6 % 2 is 0

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Relational operators

These perform comparisons and the result is what is called a boolean: a value TRUE or FALSE

FALSE is represented by 0; anything else is TRUE

The relational operators are: < (less than) <= (less than or equal to) > (greater than) >= (greater than or equal to) == (equal to) != (not equal to)

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Logical operators(also called Boolean operators)

These have Boolean operands and the result is also a Boolean.

The basic Boolean operators are: && (logical AND) || (logical OR) ! (logical NOT) -- unary

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Assignment operator: =

Binary operator used to assign a value to a variable.

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Remember, an expression results a value. So, what is the result of an assignment expression?

The value of an assignment expression is its right operande.g.

int a=10; cout << a=7;

Output: 7 (not 10). Because the value of expression a=7 is 7 (i.e its right operand)

Assignment is a special expression. Beside results a value, it also does other thing which is putting the value into its

left operand. This is called a side effect.

In the previous example, a side effect has occurred to variable a after evaluating the assignment expression (a=7). Now, the variable has a new value which is 7.

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Special assignment operators

write a += b; instead of a = a + b; write a -= b; instead of a = a - b; write a *= b; instead of a = a * b; write a /= b; instead of a = a / b; write a %= b; instead of a = a % b;

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Special assignment operators

Increment, decrement operators: ++, -- Instead of a = a + 1 you can write a++ or ++a Instead of a = a - 1 you can write a-- or --a

These operators cause side effect What is the difference?

num = 10;ans = num++;

num = 10;ans = ++num;

First increment num,then assign num to ans.In the end,

num is 11ans is 11

First assign num to ans,then increment num.In the end,

num is 11ans is 10

post-increment pre-increment

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Result of postfix Increment

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Result of Prefix Increment

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Precedence & associativity

How would you evaluate the expression 17 - 8 * 2 ?

Is it 17 - (8 * 2)or (17 - 8) * 2 ?

These two forms give different results. We need rules!

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When two operators compete for the same operand (e.g. in 17 - 8 * 2 the operators - and * compete for 8) the rules of precedence specify which operator wins. The operator with the higher precedence wins

If both competing operators have the same precedence, then the rules of associativity determine the winner.

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! Unary – * / %

+ – < <= >= >

= = !=

&&

||

=

higher precedence

lower precedence

Associativity: execute left-to-right (except for = and unary – )

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Example: Left associativity

3 * 8 / 4 % 4 * 5

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Example: Right associativity

a += b *= c-=5

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Examples: X =17 - 2 * 8 Ans: X=17-(2*8) , X=1

Y = 17 - 2 - 8 Ans: Y = (17-2)-8, Y=7

Z = 10 + 9 * ((8 + 7) % 6) + 5 * 4 % 3 *2 + 1 ?

Not sure? Confused? then use parentheses in your code!

Technology

03 1 Operators And Expressions