CS Class 07 Topics –  When software goes wrong  Count controlled loops  Sentential controlled loops  putting it all together Announcements  Programming Project 1 due Thurs. by midnight ( to  Exam 1 – New date??  Read pages ( ) for next time

FYI iostream is a header file using for input/output in C++ that is part of the C++ standard library  Collection of classes, constants, functions, objects and templates If you didn’t have using namespace std  You would need to add std:: in front of cout to tell it to use the std (standard) library  e.g. std::cout << “hello” << endl;  more than on library can use same name

When software goes wrong… What does software do?  Payrolls, bills, businesses…  Phones & other ‘net’ systems  Elevator controls  Anti-lock brake controllers  Insulin pumps, heart pacemakers  X-ray therapy equipment  Aircraft control (“fly by wire”) What happens when software fails?  Bills and paychecks wrong  When phones die…  Elevators…  Auto brakes…  Insulin pumps…  X-ray machines with bad software have killed Therac-25 (100 times dose)  Aircraft Commercial passenger planes have crashed

How important is it for software to work? If software doesn’t work,  Things go wrong,  Businesses fail,  People lose their jobs,  People are injured,  People even die… Many people have died!

How can we make software work? Careful planning: algorithms, good teaming skills, good communication Teaching those skills Making sure students know what we’re teaching.

Class exercises Write a C++ program that reads in five integers and prints out their product (the result of multiplying them together)  Example , output , output , output 12 Write a C++ program that reads in two integers and prints out all the numbers from the first to the second  The first value read will always be less than (or equal to) the second  Example 8 13 Output: Important: Figure out your algorithm (on paper) before you start to code these problems.

Count-controlled loops You know exactly how many times the loop will execute  Have this value in a variable Example int main( ) { int num, count = 0, sum = 0; while (count < 10) { cout << “Enter a num: ”; cin >> num; sum = sum + num; count = count + 1; } cout << “The sum is :” << sum << endl; return 0; }

Don’t know when the data will stop, you just know the last value. Sentinel-controlled loops (input) Read data until input is –1 int main( ) { int sum=0, data; cout<< “Enter data (-1 to quit)” << endl; cin >> data; while (data != -1) { sum = sum + data; cin >> data; } cout << “Sum is: “ << sum << endl; return 0; } –1

Class exercise Write a C++ program that reads in a sequence of 1’s and 0’s, stopping when the value 2 is read, and then prints out the value that occurred the most often.  Consider the algorithm: This is only a minor change from the previous example.  What needs to change?

Tracing – What is the output? #include using namespace std; int main ( ) { int k = 0, num = 1; while (k < 4) { cout << num << endl; k = k + 1; num = num * 10; } cout << "final num = " << num << endl; return 0; }

Tracing What is output by the program below? #include using namespace std; int main ( ) { int k = 0, num = 1; while (k < 4) { cout << num << endl; k = k + 1; num = num * 10; } cout << "final num = " << num << endl; return 0; } knumOutput final num = 10000

More tracing #include using namespace std; int main( ) { int a= 5, b = 0; while (a > 0) { cout << a << “ “; cout << b << endl; b = b + a; a = a – 1; } cout << b << endl; return 0; } Variables Output AB

Class exercises (do at least two) Write a C++ program that reads in 20 integers, counts the number of odd and even numbers, and prints out the number of odd and even numbers  Hint: what does num%2 do? Write a C++ program that reads in 10 integers and prints out the largest and smallest values seen Write a C++ program that reads in 20 characters (you will only see vowels in the input – a, e, i, o, and u) and prints out the vowel that occurred the most often Important: figure out your algorithm before you start to code these problems

End of Class 07 Read pages for next time If you have not yet read Chapters 1, 2 & 3 you need to do it now.