1. Input Based Programs

2. Generic Algorithm
Algorithm for every program ever written:

3. Generic Algorithm Algorithm for every program ever written:
Get some input
Do some stuff to it
Output a value

4. Getting Input cin : console input
"Read from the console into variable1"
>> : stream extraction operator

5. Prompt Lines Prompt for input with cout before doing cin:
cout << "Please enter a number between 1 and 10 and "
<< "press the return key" << endl;
int num;
cin >> num;

6. Bad Input
Bad input = silent failure!!! Variable maintains previous value int x; cin >> x;
Input
Result 12
X is set to 12 Q
X is ??? program continues .5
12.5
X is set to 12 ".5" is saved for next needed input

7. Bad Input
Bad input = silent failure!!! No more input accepted int x, y; cin >> x; cin >> y;
Input
Result
12 2
X is set to 12, y to 2 12 2
12 Q
X is 12 y is ????
Q 12
X and Y are ????

8. Bad Input
Bad input = silent failure!!! No more input accepted int x, y; cin >> x; cin >> y;
Input
Result
12 Q
X is 12 y is ????
Q 12
X and Y are ????

9. Don't worry about bad input
For now…
Don't worry about bad input
Don't attempt to "catch" bad input on assignments
No "try again" input loops, no "are you sure", no "run again?", etc…
DO make sure you accept the input a problem specifies

10. Software Development Lifecycle
The grand process:

11. Software Development Lifecycle
Small scale
Understand problem
Decide on inputs and outputs
How many, what types, what order
Start program
Read in inputs into variables
Do math on variables, store results into new variables
Output variables that contain answers

12. Software Development Lifecycle
Testing:
Test early and often
Read in values – confirm you got them correctly
Partway through calculations
Work in small steps
NO: double answer = (-b + pow( pow(b,2) – 4 * a * c), 0.5) / (2.0 * a);
YES: double bSquared = pow (b, 2); double discriminant = bSquared – 4 * a * c double twoA = 2.0 * a; double answer = (-b + pow(discriminant, 0.5)) / twoA;

13. Sample 1
Given the lengths of the two legs of a triangle, print the length of the hypotenuse.
Sample run:
Input side A: 3 Input side B: 4 Hypotenuse is 5.0

14. Sample 1
Given the lengths of the two legs of a triangle, print the length of the hypotenuse.
Input: side lengths a and b
Output: hypotenuse

15. Sample 2
Ask the ctime library for number of seconds since Midnight, Jan 1st Print the time of day like hour:minute:second.

16. Sample 2
Ask the ctime library for number of seconds since Midnight, Jan 1st Print the time of day
Input: None from user. (Get time from library)
Output: hours, minutes, seconds