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1 Chapter 3:Operators and Expressions| SCP1103 Programming Technique C | Jumail, FSKSM, UTM, 2006 | Last Updated: July 2006 Slide 1 Operators and Expressions Lecture 3 by Jumail Bin Taliba Faculty of Computer Science & Information System

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2 Chapter 3:Operators and Expressions| SCP1103 Programming Technique C | Jumail, FSKSM, UTM, 2006 | Last Updated: July 2006 Slide 2 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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3 Chapter 3:Operators and Expressions| SCP1103 Programming Technique C | Jumail, FSKSM, UTM, 2006 | Last Updated: July 2006 Slide 3 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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4 Chapter 3:Operators and Expressions| SCP1103 Programming Technique C | Jumail, FSKSM, UTM, 2006 | Last Updated: July 2006 Slide 4 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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5 Chapter 3:Operators and Expressions| SCP1103 Programming Technique C | Jumail, FSKSM, UTM, 2006 | Last Updated: July 2006 Slide 5 Some types of statement in C++

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6 Chapter 3:Operators and Expressions| SCP1103 Programming Technique C | Jumail, FSKSM, UTM, 2006 | Last Updated: July 2006 Slide 6 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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7 Chapter 3:Operators and Expressions| SCP1103 Programming Technique C | Jumail, FSKSM, UTM, 2006 | Last Updated: July 2006 Slide 7 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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8 Chapter 3:Operators and Expressions| SCP1103 Programming Technique C | Jumail, FSKSM, UTM, 2006 | Last Updated: July 2006 Slide 8 Binary expression

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9 Chapter 3:Operators and Expressions| SCP1103 Programming Technique C | Jumail, FSKSM, UTM, 2006 | Last Updated: July 2006 Slide 9 Unary Expression

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10 Chapter 3:Operators and Expressions| SCP1103 Programming Technique C | Jumail, FSKSM, UTM, 2006 | Last Updated: July 2006 Slide 10 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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11 Chapter 3:Operators and Expressions| SCP1103 Programming Technique C | Jumail, FSKSM, UTM, 2006 | Last Updated: July 2006 Slide 11 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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12 Chapter 3:Operators and Expressions| SCP1103 Programming Technique C | Jumail, FSKSM, UTM, 2006 | Last Updated: July 2006 Slide 12 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 2 5 / 2 There is no promotion occurred. Both operands are the same type.

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13 Chapter 3:Operators and Expressions| SCP1103 Programming Technique C | Jumail, FSKSM, UTM, 2006 | Last Updated: July 2006 Slide 13 Arithmetic operators: +, * + is the addition operator * is the multiplication operator They are both binary

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14 Chapter 3:Operators and Expressions| SCP1103 Programming Technique C | Jumail, FSKSM, UTM, 2006 | Last Updated: July 2006 Slide 14 Arithmetic operator: This operator has two meanings: subtraction operator (binary) negation operator (unary) e.g. 31 - 2 e.g. -10

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15 Chapter 3:Operators and Expressions| SCP1103 Programming Technique C | Jumail, FSKSM, UTM, 2006 | Last Updated: July 2006 Slide 15 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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16 Chapter 3:Operators and Expressions| SCP1103 Programming Technique C | Jumail, FSKSM, UTM, 2006 | Last Updated: July 2006 Slide 16 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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17 Chapter 3:Operators and Expressions| SCP1103 Programming Technique C | Jumail, FSKSM, UTM, 2006 | Last Updated: July 2006 Slide 17

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18 Chapter 3:Operators and Expressions| SCP1103 Programming Technique C | Jumail, FSKSM, UTM, 2006 | Last Updated: July 2006 Slide 18

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19 Chapter 3:Operators and Expressions| SCP1103 Programming Technique C | Jumail, FSKSM, UTM, 2006 | Last Updated: July 2006 Slide 19 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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20 Chapter 3:Operators and Expressions| SCP1103 Programming Technique C | Jumail, FSKSM, UTM, 2006 | Last Updated: July 2006 Slide 20

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21 Chapter 3:Operators and Expressions| SCP1103 Programming Technique C | Jumail, FSKSM, UTM, 2006 | Last Updated: July 2006 Slide 21 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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22 Chapter 3:Operators and Expressions| SCP1103 Programming Technique C | Jumail, FSKSM, UTM, 2006 | Last Updated: July 2006 Slide 22

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23 Chapter 3:Operators and Expressions| SCP1103 Programming Technique C | Jumail, FSKSM, UTM, 2006 | Last Updated: July 2006 Slide 23 Assignment operator: = Binary operator used to assign a value to a variable.

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24 Chapter 3:Operators and Expressions| SCP1103 Programming Technique C | Jumail, FSKSM, UTM, 2006 | Last Updated: July 2006 Slide 24 Remember, an expression results a value. So, what is the result of an assignment expression? The value of an assignment expression is its right operand e.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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25 Chapter 3:Operators and Expressions| SCP1103 Programming Technique C | Jumail, FSKSM, UTM, 2006 | Last Updated: July 2006 Slide 25 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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26 Chapter 3:Operators and Expressions| SCP1103 Programming Technique C | Jumail, FSKSM, UTM, 2006 | Last Updated: July 2006 Slide 26 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 11 ans is 11 First assign num to ans, then increment num. In the end, num is 11 ans is 10 post-increment pre-increment

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27 Chapter 3:Operators and Expressions| SCP1103 Programming Technique C | Jumail, FSKSM, UTM, 2006 | Last Updated: July 2006 Slide 27 Result of postfix Increment

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28 Chapter 3:Operators and Expressions| SCP1103 Programming Technique C | Jumail, FSKSM, UTM, 2006 | Last Updated: July 2006 Slide 28 Result of Prefix Increment

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29 Chapter 3:Operators and Expressions| SCP1103 Programming Technique C | Jumail, FSKSM, UTM, 2006 | Last Updated: July 2006 Slide 29 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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30 Chapter 3:Operators and Expressions| SCP1103 Programming Technique C | Jumail, FSKSM, UTM, 2006 | Last Updated: July 2006 Slide 30 Precedence & associativity 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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31 Chapter 3:Operators and Expressions| SCP1103 Programming Technique C | Jumail, FSKSM, UTM, 2006 | Last Updated: July 2006 Slide 31 Precedence & associativity ! Unary – * / % + – = > = = != && || = higher precedence lower precedence Associativity: execute left-to- right (except for = and unary – )

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32 Chapter 3:Operators and Expressions| SCP1103 Programming Technique C | Jumail, FSKSM, UTM, 2006 | Last Updated: July 2006 Slide 32 Example: Left associativity 3 * 8 / 4 % 4 * 5

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33 Chapter 3:Operators and Expressions| SCP1103 Programming Technique C | Jumail, FSKSM, UTM, 2006 | Last Updated: July 2006 Slide 33 Example: Right associativity a += b *= c-=5

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34 Chapter 3:Operators and Expressions| SCP1103 Programming Technique C | Jumail, FSKSM, UTM, 2006 | Last Updated: July 2006 Slide 34 Precedence & associativity 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!

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