SMS 3515: Scientific Computing. Sem /2015

Transcription

1 s s SMS 3515: Scientific Computing Department of Computational and Theoretical Sciences, Kulliyyah of Science, International Islamic University Malaysia. Sem /2015 The if s

2 that are conceptually either true or false. Also called as Boolean expressions or logical expressions. Can use both relational and logical operators. In, true is represented by the logical value 1, and false is represented by the logical value 0. Exclusive-or function xor : returns logical true if one (and only one) of the arguments is true. Table 1 : List of relational and logical operators in. Operator Meaning > greater than < less than >= greater than or equals <= less than or equals == equality = inequality or (for scalars) && and (for scalars) not s The if s

3 s Table 2 : Operator Precedence Rules in. Operator parantheses ( ) transpose and power negation and not multiplication and division \, / addition + and substraction colon operator : relational <, <=, >, >=, ==, = and && or assignment = Precedence highest lowest The if s

4 The if s The if statement chooses whether another statement, or group of statements, is executed or not. General form of if statement : if condition action Condition : a relational expression that is conceptually or logically true or false. Action : statement/s that will be executed if the condition is true. The if s

5 Be careful when writing condition involving logical operation. For example, to process an input for yes/no question, the letter y can be written in lowercase y or uppercase Y. In order to write the condition, one should write letter == Y letter == y instead of letter == Y y because the second condition would always be true, regardless of the value of the variable letter. s The if s

6 s statement is used to choose between two statements, or sets of statements. General form : if condition action1 else action2 Common application : error checking. The if s

7 s if condition1 action1 else if condition2 action2 else if condition3 action3 else action4 s The if s

8 The elseif Clause s if condition1 action1 elseif condition2 action2 elseif condition3 action3 % etc: there can be many of these else actionn % the nth action The if s

9 The swith A switch statement can often be used in place of a nested if-else or an if statement with many elseif clauses. Used when an expression is tested to see whether it is equal to one of several possible values or sometimes for the error message. General form : switch switch_expression case caseexp1 action1 case caseexp2 action2 case caseexp3 action3 % etc: there can be many of these otherwise actionn s The if s

10 s menu displays a Figure Window with pushbuttons for the options. General form: variablename = menu( heading, pushbutton1..., pushbutton2, pushbutton3 ) returns the number of the button that is pushed. The if s

11 The is s isletter : return logical 1 if the character argument is a letter of the alphabet, or 0 if it is not. isempty : return logical true if a variable is empty, logical false if it has a value, or an error message if the variable does not exist. This also true for string. iskeyword : determine whether or not a name is a key word in. The if s