CSEC1003 - Secure Coding Lecture 03 - Selection PDF

CSEC1003 - Secure Coding Lecture 03 Selection 1  Agenda  Boolean operators  Logical operations  Relational operations  Equality operations  If statements  Basics  Nesting  Examples  Switch statements  Basics ...

CSEC1003 - Secure Coding Lecture 03 Selection 1  Agenda  Boolean operators  Logical operations  Relational operations  Equality operations  If statements  Basics  Nesting  Examples  Switch statements  Basics  Examples  Example:  A simple calculator  A computer program is a sequence of instructions which perform a task  We call these sets of instructions algorithms  A written or verbal set of a logical sequence of instructions  Typically algorithms are made up of three structural components:  Sequence  Step 1 happens before step 2 which happens before step 3  Selection  Sometimes a choice has to be made between two or more options  This can lead to the algorithm having branches  Iteration  The repeating of an instruction or a sequence of instructions  Can stop after a set number or on a certain condition  You can use these in combination to solve nearly all  In last lecture we saw variables including Boolean variables  Boolean operators  Used to find the logical value of some expression  && and  || or  ! Not  == equal to  != not equal to  > greater than  < less than  >= great than or equal to  Two Boolean variables: bool male = true; bool athlete = true;  What do the following mean: athlete && male; // athlete & male !athlete && male; athlete && !male; !athlete && !male; !(athlete && male); athlete || male; // athlete or male !athlete || male; athlete || !male; !athlete || !male; !(athlete || male);  De Morgan’s Laws The negation of a conjunction is the disjunction of the negations not (A and B) is the same as (not A) or (not B) !athlete && !male == !(athlete || male); not (A or B) is the same as (not A) and (not B) !(athlete || male) == !athlete && ! male;  What do the following mean: bool gt = 0 > 9; bool lt = 0 < 9; bool gte = 9 >= 9; bool lte = 14 9; // false bool lt = 0 < 9; // true bool gte = 9 >= 9; // true bool lte = 14 ‘n’; bool lt2 = ‘0’ < ‘9’;  What do the following mean: bool gt = 0 > 9; // false bool lt = 0 < 9; // true bool gte = 9 > 9; // true bool lte = 14 < 15; // true bool gt2 = ‘y’ > ‘n’; // true bool lt2 = ‘0’ < ‘9’; // true int a = 5; bool between = 0 < a && a < 10  Allow conditional branches in programs  If some condition is true then do something  If that condition is not true then do something else Previou  Flow diagram: s stateme nt If (expression) Statement tru e fals e Next statement  Allow conditional branches in programs  If some condition is true then do something  If that condition is not true then do something else  Syntax: if (Boolean condition) { Do stuff in here if condition is true }  Allow conditional branches in programs  If some condition is true then do something  If that condition is not true then do something else  Syntax: if (Boolean condition) { Do stuff in here if condition is true }  Example: int num = 4; if(num == 4) {  Else part of the if statement only runs when condition is not met:  Syntax: if (Boolean condition) { Do stuff in here if condition is true } else { Do stuff in here if condition is false }  Else part of the if statement only runs when condition is not met:  int Example: num 4; = if(num 4) == { // Only do when num == } this 4 cout