Relational Operators, and the If Statement. 9.1 Combined Assignments. Relational Operators (4.1) Last time we discovered combined assignments such as:

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1 Relatinal Operatrs, and the If Statement 9/18/06 CS150 Intrductin t Cmputer Science Cmbined Assignments Last time we discvered cmbined assignments such as: a /= b + c; Which f the fllwing lng frms is equivalent t the abve frm? a = a / b + c; a = a / (b + c); Assume that: a = b = 6, c = 9 9/18/06 CS150 Intrductin t Cmputer Science 1 2 Relatinal Operatrs (4.1) S far, we can Input, Output and Calculate Hw can we explre relatinships between data? Is yur grade greater than 90%? Is it htter r clder tday than yesterday? D I have enugh US dllars t get 100 Eurs? 9/18/06 CS150 Intrductin t Cmputer Science 1 3 1

2 Relatinal Operatrs, Explained! Operatr > Meaning Greater than < Less than >= Greater than r equal t <= Less than r equal t == Equal t!= Nt equal t All are binary peratrs Left t right assciativity 9/18/06 CS150 Intrductin t Cmputer Science 1 4 Relatinal Expressin An expressin is a statement that has value Relatinal expressin: an expressin that uses a Relatinal Operatr its value is a Blean value (True r False) int x = 9, y = 42; x > y y == x // y = x; is the assignment peratr x <= (x * y + 99) 9/18/06 CS150 Intrductin t Cmputer Science 1 5 Precedence (page 1125) Precedence Operatrs (Highest t Lwest) (unary negatin) - Arithmetic Operatrs * / % + - > >= < <= Relatinal Operatrs ==!= = += -= *= /= %= Assignment Operatrs 9/18/06 CS150 Intrductin t Cmputer Science 1 6 2

3 9.2 Practice What is the value f the fllwing Relatinal Expressins? int x = 99, y = 42; x > y y <= x y!= x x == (x + 1) y == y + 1 9/18/06 CS150 Intrductin t Cmputer Science 1 7 Blean value (True r False) Hw des the cmputer represent True and False? New data type: bl bl btvalue = true; // 1 bl bfvalue = false; // 0 9/18/06 CS150 Intrductin t Cmputer Science Practice bl bvalue; int x = 5, y = 10; bvalue = x > y; // value =?? bvalue = x == y; // value =?? bvalue = x == y - 5; // value =?? // what des this utput lk like? cut << Value is: << bvalue; 9/18/06 CS150 Intrductin t Cmputer Science 1 9 3

4 UML Activity Diagrams UML: Unified Mdelling Language Used t represent algrithms that will later be translated int cde Give the prgrammer a visual representatin f the slutin t a prblem Can als help the prgrammer see a slutin t a prblem 9/18/06 CS150 Intrductin t Cmputer Science 1 10 Example Write a prgram that will read in the current temperature in degrees Fahrenheit and cnvert it int Celsius display message asking user fr temperature in Fahrenheit read in temperature and stre it cnvert temperature t Celsius display temperature in Celsius 9/18/06 CS150 Intrductin t Cmputer Science 1 11 The if Statement (4.2) We execute each statement in ur prgram in rder int x=5, y=10; What if we nly want t execute a statement if(x > y) smetimes? The if Statement! // d stuff 9/18/06 CS150 Intrductin t Cmputer Science

5 Frmally defined if(expressin) statement 1; statement 2;... statement n; What is an expressin? Just like a functin, start at the tp and execute in rder t the bttm 9/18/06 CS150 Intrductin t Cmputer Science 1 13 UML Activity Diagram if( grade > 59 ) cut << passed! ; [grade > 59] utput passed! [grade <= 59] 9/18/06 CS150 Intrductin t Cmputer Science Practice int x = 5, y = 10; bl bvalue = x > y; if (bvalue) cut << value is True << endl; if (x < y) cut << x << < << y; cut << is true << endl; 9/18/06 CS150 Intrductin t Cmputer Science

6 Cding Standards if(expressin) statement 1; if(expressin) statement 1; If yu nly have ONE statement in the bdy f the if, the are ptinal in C++. Fr this class, the must ALWAYS be used. Nt using will result In a lss f style pints. The must als be n their wn line. Why? 9/18/06 CS150 Intrductin t Cmputer Science Mre n Truth Expressins that evaluate t nn-zer are cnsidered true int x = 5, y = 0; if (x + y) // This will be executed cut << x + y is True << endl; if (y) // This will NOT be executed cut << y is True << endl; 9/18/06 CS150 Intrductin t Cmputer Science Example Yur lcal bkstre has asked yu t write a prgram t help them determine the cst f shipping f custmers rders. If the rder is $30 r less then shipping will cst $5, if the rder is ver $30 then shipping will be $3. 9/18/06 CS150 Intrductin t Cmputer Science

7 Slutin duble rder, shipping; cut << "Enter the amunt f the rder: "; cin >> rder; if( rder <= 30 ) shipping = 5.00; if( rder > 30 ) shipping = 3.00; cut << "The cst f shipping is $" << shipping << endl; return 0; 9/18/06 CS150 Intrductin t Cmputer Science Practice The bkstre has nw changed it s shipping plicy s that If the rder is $30 r less, shipping is $5 If the rder is ver $30 but less than r equal t $50, shipping is $3 If the rder is ver $50 then shipping is $2 What wuld we need t change in the prgram? 9/18/06 CS150 Intrductin t Cmputer Science 1 20 Flating Pint and Relatinal Operatrs Flating pint math may nt wrk ut as yu expect because f rund ff errrs. In Math 6 * 2/3 = 4 In C++, where is equivalent t 2/3 6.0 * = 6.0 * = 6.0 * = 6.0 * ( 2.0 / 3.0 ) = 9/18/06 CS150 Intrductin t Cmputer Science

9.8 Example (page 180) duble result; result = 6.0 * 0.666666; if ( result == 4.0 ) cut << result == 4.

8 9.8 Example (page 180) duble result; result = 6.0 * ; if ( result == 4.0 ) cut << result == 4.0 << endl; cut << setprecisin(6) << fixed; cut << result << endl; cut << setprecisin(2) << result; cut << endl; 9/18/06 CS150 Intrductin t Cmputer Science 1 22 Example 9/18/06 CS150 Intrductin t Cmputer Science 1 23 Flating Pints in Relatinal Operatrs Hw can we get arund this prblem? 9/18/06 CS150 Intrductin t Cmputer Science

9 Blean Flags We have seen hw t stre the value f a relatinal expressin t a bl variable. bl bissquare = ( length == width); if ( bissquare ) Why wuld yu want t d this? Why nt use the relatinal expressin directly? 9/18/06 CS150 Intrductin t Cmputer Science 1 25 Blean Flags This use f a bl variable is called a flag. It is used t keep track f a cnditin s that the expressin is evaluated nly nce 9/18/06 CS150 Intrductin t Cmputer Science

CS1150 Principles of Computer Science Midterm Review

CS1150 Principles of Computer Science Midterm Review CS1150 Principles f Cmputer Science Midterm Review Yanyan Zhuang Department f Cmputer Science http://www.cs.uccs.edu/~yzhuang CS1150 UC. Clrad Springs Office hurs 10/15, Mnday, 12:05 12:50pm 10/17, Wednesday