Input Based Programs

Generic Algorithm Algorithm for every program ever written:

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

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

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;

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

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 ????

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 ????

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

Software Development Lifecycle The grand process:

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

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;

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

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

Sample 2 Ask the ctime library for number of seconds since Midnight, Jan 1st 1970. Print the time of day like hour:minute:second.

Sample 2 Ask the ctime library for number of seconds since Midnight, Jan 1st 1970. Print the time of day Input: None from user. (Get time from library) Output: hours, minutes, seconds