Random notes from Week 12 Lecture - 4-9-07

*   reminder: a Python function...

#-----
# contract: get_hypotenuse: number number -> number

# purpose: compute and return the length of the hypotenuse
#          of a right triangle whose two "other" sides
#          are of length <side1>, <side2>

# examples: get_hypotenuse(3, 4) == 5
#           get_hypotenuse(3, 7) == 7.62

from math import *

def get_hypotenuse(side1, side2):
    return sqrt( pow(side1, 2) + pow(side2, 2) )
#-----

*   ...and its C++ equivalent:

//-----
/*
# contract: get_hypotenuse: double double -> double

# purpose: compute and return the length of the hypotenuse
#          of a right triangle whose two "other" sides
#          are of length <side1>, <side2>

# examples: get_hypotenuse(3, 4) == 5
#           get_hypotenuse(3, 7) == 7.62
*/

#include <cmath>
using namespace std;

double get_hypotenuse (double side1, double side2)
{
    return sqrt( pow(side1, 2) + pow(side2, 2) );
}
//----- 

*   SO: moving on and talking about if statements ---

*   ... the basic FLOW CHART is the same for both C++'s and Python's
    if statement!

    ...just the SYNTAX differs.

*   the differences in their syntax:

    *   in C++, you GOTTA put an overall set of parentheses
        around the if-condition

    *   in C++, you DON'T need a colon after the condition

    *   in C++, exactly ONE statement follows the if and condition,

        BUT! in C++, you can always consider a BLOCK* to be a single
	statement

	(* a BLOCK is a {, as many statements as you want, and a } --
        COURSE STYLE: each {, } are on their OWN line,
        lined up with preceding and following lines,
	and statements WITHIN are indented by 3 or more spaces)

    *   SO:

        if (val < 3)
        {
            sum = sum + val;
            return true;
        }

    *   ...oh yes, and in C++ don't forget the ; after each action

PYTHON:
    if grade < 0:
        return -1
C++:
    if (grade < 0)
    {
        return -1;
    }

    *   there is no elif in C++ (but else if (cond) is fine)

    *   the else is optional in both C++ and Python,
        but in C++, DON'T put a colon after the else.   

PYTHON:
    if grade < 0:
        return -1
    elif grade > 0:
        return 1
    else:
        return 0

C++:
    if (grade < 0)
    {
        return -1;
    }
    else if (grade > 0)
    {
        return 1;
    }
    else
    {
        return 0;
    }


LECT EX #1: translate this PYTHON fragment into C++
(assume all functions already available and defined)

    PYTHON:

    if (worked_overtime(hrs_worked) == True):
        return (reg_owed(hrs_worked) + 
                overtime_owed(hrs_worked - OVERTIME_LIMIT))
    else:
        return reg_owed(hrs_worked)


*   what about while loops?

    *   again, the semantics are the same!! (flow chart would
        be the same)

    *   only the syntax differs:

        *   in C++, you've GOT to have parentheses around the
            overall while condition

        *   in C++, you don't have a colon after the while condition

        *   in C++, it expects exactly 1 "statement" after the
            while (but you can use a BLOCK wherever you can use
	    a statement)

ASIDE: a C++ local variable must be DECLARED (and set to something)
       before USING it...

       type variable_name;
       type variable_name = init_value;

PYTHON:
    sum = 0
    count = 0
    while count < 10:
        sum = sum + count
        count = count + 1
    return sum 

C++:
    int sum = 0;
    int count = 0;
    while (count < 10)
    {
        sum = sum + count;
        count = count + 1;
    }
    return sum;

*   what if we'd like to throw in a little screen output?

    ...in C, C++, input and output are actually not part of
       the base language --- they are provided by libraries;

    ... the C++ iostream library provides some simple input/output

        (you put:

#include <iostream>
using namespace std;
      
         ...to use goodies from the iostream library

    SO: to print something to the screen:

     cout << "value";

          ^ stream operator

     cout << "value" << (3 + 5) << endl;        

             ^ print value
                        ^ print 8
                                   ^ and end it with a newline

     cout << "\n";
              ^ this prints a newline, too

cout << "value" << (3 + 5) << endl;
value8

      Note: if you put a variable name in, it prints the VALUE
      of that variable

int i = 7;
cout << i;
i = i + 3;
cout << i;

710

Lect Ex #3: write a count-controlled loop that prints HELLO to
the screen 7 times, EACH on its own line (no named constant required
JUST for this syntax-lecture-exercise...)

How about input?

*   in the C++ iostream standard, there's an object cin

    cin >> variable;

    ... next thing typed by the user, C++ will try valiantly
        to convert to variable's type and and set variable to

    int val;
    cout << "type something";
    cin >> val;