EECS 183. Week 3 - Diana Gage. www-personal.umich.edu/ ~drgage

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1 EECS 183 Week 3 - Diana Gage www-personal.umich.edu/ ~drgage

2 Upcoming Deadlines Lab 3 and Assignment 3 due October 2 nd (this Friday) Project 2 will be due October 6 th (a week from Friday) Get started early!

3 New Material: Conditionals What is a conditional? A statement with a condition If something evaluates to true, we want to do one thing If that thing evaluates to false, we want to do something else ^ general idea

4 New Operations and Operators && and or! not (negation) = assignment operator == comparison operator

5 New Operations and Operators < less than > greater than <= less than or equal to >= greater than or equal to!= not equal to

6 Example: if statement int age = 23; if (age >= 18) { cout << You can get a tattoo! ; cout << endl;

7 && -- The and operator Both pieces of the conditional must evaluate to true Sample code: if (sunny && above_60) { cout << Let s throw a disc outside! ; cout << endl; Both must be true

8 I I The or operator One or more pieces of the conditional must evaluate to true Sample code: if (sunny above_60) { cout << I guess we can throw a disc outside ; cout << endl; One, or the other, or both, must be true

9 ! The not operator This is the negation operator It takes the truth value of the variable or expression in question, and negates it bool has_green_hair = true; cout <<!has_green_hair << endl; What does this print?

10 ! The not operator This is the negation operator It takes the truth value of the variable or expression in question, and negates it bool has_green_hair = true; cout <<!has_green_hair << endl; What does this print? 0

11 if, else if, else statements Often conditionals are a group of statements comprised of: if ( ) { else if ( ) { (there can be many else ifs) else { These are called branches Notice how the else statement does not have parentheses Catch all à doesn t need condition

12 Branching Statements are dependent on each other in the order the code is written The else if follows directly from the if, and the else follows from both the if and else if

13 Branching if ( ) { This always goes first, and it will either execute (if true) or not (if false) else if ( ) { ) This runs only if the previous if statement did not execute else { This runs only if neither of the previous statements executes This will ALWAYS execute if neither of the previous statements did

14 Example of Branching: if (sunny && above60) { cout << Let s play outside! << endl; else if (rainy) { cout << Let s watch a movie! ; cout << endl; else { cout << I can t decide! << endl;

15 Branching There can be as many else ifs as you want But only one if and one else per branch This doesn t mean you can t have many if statement in a row Each will always execute, regardless of the previous one Sometimes this is what you want!

16 = The Assignment Operator This operator assigns whatever is on the left to whatever is on the right int k = 25;

17 == The Comparison Operator This operator compares whatever is on the left to whatever is on the right This comparison will evaluate to true or false Either the two sides are the same, or not Be careful with the difference between = and ==

18 IMPORTANT difference: = vs. == Be careful not to use the assignment operator within a conditional Instead of checking whether they are the same (true) or different (false) The line of code will set the left equal to whatever was on the right This is probably not what you want

19 Common error: = vs. == // Let s say the following code is in a function int a = 30; int b = 25; if (a == b) { cout << equal << endl; return true; if (a = b) { cout << equal << endl; return true;

20 Common error: = vs. == // Let s say the following code is in a function int a = 30; int b = 25; if (a == b) { cout << equal << endl; return true; The if statement won t execute because a is not equal to b if (a = b) { cout << equal << endl; return true;

21 Common error: = vs. == // Let s say the following code is in a function int a = 30; int b = 25; if (a == b) { cout << equal << endl; return true; if (a = b) { cout << equal << endl; return true;

22 Common error: = vs. == // Let s say the following code is in a function int a = 30; int b = 25; if (a == b) { cout << equal << endl; return true; if (a = b) { cout << equal << endl; return true; - a will be set to 25 - the value 25 is true - the statements inside will execute - but that s incorrect!

23 Important Difference: x < y < z vs. x < y && y < z Reminder: Anything but 0 à true 0 à false You want to use x < y && y < z because

25 Short-circuit evaluation bool print_hello() { cout << Hello << endl; return true; int main() { bool sunny = true; if (sunny && print_hello()) { cout << It s sunny and we said hello! ; else if (sunny print_hello()) { cout << it s sunny, or we said hello, or both! ; else { cout << It s not sunny and we didn t say hello. ; What happens? What prints?

26 Short-circuit evaluation bool print_hello() { cout << Hello << endl; return true; int main() { bool sunny = true; if (sunny && print_hello()) { cout << It s sunny and we said hello! ; else if (sunny print_hello()) { cout << it s sunny, or we said hello, or both! ; else { cout << It s not sunny and we didn t say hello. ; Because of short-circuit evaluation, if the first element in an or statement conditional evaluates to true, the rest of the conditional won t even be checked

27 Style with Conditionals Do not do if (true) or if (a == false) Do not compare doubles Do not compare things of different types i.e. string and doubles Use consistent brackets Don t over-complicate expressions if (!(a == b)) vs. if (a!= b)

28 Quick Note: RME Requires Clause You are the programmer. You write the function. A client calls this function. The programmer should write the function assuming provided input will follow the Requires clause. Client s job to read the RME of any function they use. If they violate the requires clause, the program will still run, but may have undefined behavior. Example: // Requires: denominator is not 0 double divide (int numerator, int denominator);

29 Lab Two parts: Exam Practice Answer the question in lab3.pdf in 10 minutes (I will time you) Write your answer with pencil and paper Testing functions This will be very important for Project 2 and beyond!

30 Exam Practice Write your answers to the question just like you will on the exam Take at most ten minutes to solve the problem. Remember you will only have 90 minutes for the upcoming exam! After the 10 minutes, we will show the answer and discuss the solution You do not need to submit the answer, but keep it to help you review!

31 Exam Practice Solution

32 Testing with functions Now complete the Testing section of the lab assignment Feel free to ask questions You need to submit this portion of the lab to the autograder to receive 5 points

33 Feel free to ask any questions after class!

EECS 183 Week 8 Diana Gage. www-personal.umich.edu/ ~drgage

EECS 183 Week 8 Diana Gage. www-personal.umich.edu/ ~drgage EECS 183 Week 8 Diana Gage www-personal.umich.edu/ ~drgage Classes! My favorite topic J Definition of a class How many different definitions can we come up with? What is a class? A class is a container