© Janice Regan, CMPT 128, Jan CMPT 128: Introduction to Computing Science for Engineering Students Introduction to branching

© Janice Regan, CMPT 128, Control Structures  Control structures are used to manage the order in which statements in computer programs will be executed  Three different approaches  In sequence  Branching  Looping

© Janice Regan, CMPT 128, Control Structures  Branch: Altering the flow of program execution by making a selection or choice  Loop: Altering the flow of program execution by repetition of a particular block of statement(s)

Branching  One way selection  Two way selection  Multiple way selection © Janice Regan, CMPT 128,

4 Flowcharts  Flowcharts use some basic symbols  To start or end a function  To contain calculations  To make decisions  To connect different parts of an algorithm

© Janice Regan, CMPT 128, One-way selection  Simplest form of a branch.  Evaluate a condition that can be True or False  If the condition is true a series of actions are executed  If the condition is false that series of actions are not executed  C and C++ implementation:  if statement

© Janice Regan, CMPT 128, Flowchart: one way selection  Write the condition that needs to be satisfied in the decision box (diamond).  Based upon the value of the condition (boolean T or F) choose what to do next  The sequence of statements to be executed if the condition is true is placed in the box condition Statement 1; Statement n; T F ⋮ C and C++ implementation if statement

© Janice Regan, CMPT 128, One-way selection  Example if statement in C and C++: setFlagOrderBoxes = 0; if (numberOfBoxes < minimumBoxInventory) setFlagOrderBoxes = 1; setFlagOrderBags = 2; // always executed  setFlagOrderBags is always set to 2, even if the condition in the if statement is false

© Janice Regan, CMPT 128, C++ Compound/Block Statement  Only one statement following the if statement is part of the if control structure  What if we need more than one statement done if the condition is true?  Must use a block of statements (also called a compound statement)  C++ uses { }, to contain all the statements in a block of statements

© Janice Regan, CMPT 128, One way selection: sample  Do a series of actions only if a given condition holds  If the condition does not hold skip the actions if (myScore > yourScore) { cout << “My score was lower than yours “; difference = yourScore – myScore; cout << “I only got “ << difference << “ less points than you did” ; } cout << “Thanks for studying with me”;

© Janice Regan, CMPT 128, Two-way selection  Evaluate a condition that can be True or False  One “Set of things to do” if the condition is true,  A different “Set of things to do” if the condition is false  C and C++ implementation:  if-else statement

© Janice Regan, CMPT 128, Flowchart: two way selection  Based upon the value of the condition (boolean T or F) choose what to do next  The sequence of statements to be executed if the condition is true is placed in the box at the right  The sequence of statements to be executed if the condition is false is placed in the box below the condition condition Statement 1; Statement n; T F Statement 1; Statement n; ⋮ ⋮ Implemented in C and C++ as an if-else statement

© Janice Regan, CMPT 128, Example of two-way selection  Example if-else statement in C and C++: if (examScore > 50) myCourseGrade = “PASS”; else myCourseGrade = “FAIL”;  NOTE: Only one statement follows the if, and one statement follows the else

© Janice Regan, CMPT 128, Two way selection in C++  Complete one of two possible series of actions  First series of actions is complete if condition is true  Second series of actions is completed if condition is false if (condition) {//Series of actions to be taken when the condition is true action 1; ⋮ action n; } else { // Series of actions to be taken when the condition is false action 1; ⋮ action n; }

© Janice Regan, CMPT 128, Two way selection in C++  CODING STANDARD: always use {} to make blocks if (X<Y && Y<Z) //Never X<Y<Z { //Series of actions to be taken when the condition is true cout < < “Y is between X and Z” ; } else { // Series of actions to be taken when the condition is false cout<<“ Y is not between X and Z”; } cout << endl << “Y is “ << Y; cout << “ X is “ << X << “ Z Is “ << Z;

© Janice Regan, CMPT 128, Truth Table && The && (And) operator EXPRESSION1 EXPRESSION2 EXPRESSION1 && EXPRESSION2 T T T T F F F T F F F F

© Janice Regan, CMPT 128, Multiple-way selection  If condition1 is true the 1 st series of actions is completed  If condition1 is false and condition2 is true the 2 nd series of actions is completed  If condition1 and condition2 are false and condition3 is true the 3 rd series of actions is completed  …  If all conditions are false the final series of actions is completed  Implemented in C++ as an if-elseif-else statement

© Janice Regan, CMPT 128, Flowchart for multiple selection condition2 Statement 1; Statement n; T F Statement 1; Statement n; condition F Statement 1; Statement n; T ⋮ ⋮ ⋮

© Janice Regan, CMPT 128, Example of Multiple selection  Example: if (examScore > 80) myCourseGrade = “A”; else if (examScore > 70) myCourseGrade = “B ”; else myCourseGrade = “FAIL”;

© Janice Regan, CMPT 128, Example of Multiple selection  Example: always use { } to create blocks if ( X > 80 || Y < 100) { cout 80, Y any value) OR (X any value, Y<100)” ; } else if (X < 80) { cout = 100” ; } else { cout = 100”; }

© Janice Regan, CMPT 128, Truth Tables || The || (Inclusive Or) operator EXPRESSION1 EXPRESSION2 EXPRESSION1 || EXPRESSION2 T TT T FT F TT F F F

© Janice Regan, CMPT 128, Selection: decision statements Each decision statement contains a condition  The condition is an expression with a logical value (true or false)  The condition is a Boolean expression  A relational expression (a type of logical expression)  Another type of logical expression  A Boolean variable or constant

© Janice Regan, CMPT 128, Binary Relational Operators C, C++  <less than  <=less than or equal to  > greater than  >= greater than or equal to  == equal to  !=not equal to  Evaluated left to right Binary Equality Operators in C, C++

© Janice Regan, CMPT 128, Relational Expressions  A type of logical expression  Combines two numbers, strings, characters to give a value of true or false  A simple relational expression is  Two numerical values combined using a binary relational operator  A more complex relational expression is  A combination of simple relational expressions

© Janice Regan, CMPT 128, Other logical expressions Other types of logical expression include  Two logical variables / constants combined with a binary logical operator  One logical variable or constant  One logical variable or constant operated on by a unary logical operator  Two relational expressions combined with a binary logical operator  …  Any more complex logical expression

© Janice Regan, CMPT 128, Binary Logical Operators C, C++  &&Logical AND  ||Logical OR  !Not  Evaluated left to right  Arguments of logical operators have values of true or false Unary Logical Operators C, C++