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a few things will help a few things will help us design our own us design our own

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a few things will help a few things will help us design our own us design our own

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a coin flippera coin flipper

"for" loop boundaries// int x is the for loop variable counting// coin flips:int x = 0;for (x=1; x<=100; x=x+1) { cout << "X in for loop: " << x << endl; }cout << "X after for loop: " << x << endl;

Domain of a variable

for (int x=1; x<=100; x=x+1) { cout << "X in for loop: " << x << endl; }cout << "X after for loop: " << x <<

endl;// error, x not useable outside for loop

#include <cstdlib>

rand( ); - "pseudo" random number

randomNumber = rand( )%10; // generate random number 0 thru 9

srand( int seed ); - seed the random number

remember...calling a library function

int ranNum;ranNum = rand( ) %2; // random one or

zero

The result of the library function is placed into ranNum. The rand()%2 function returns a random 0 or 1 as a “service”.

two problems with rand( )

1. random numbers are the same every time you run it (the algorithm starts at a consistent place)

2. rand( )%2 gives equally spaced 0s and 1s (not random for these low numbers) on old computers (32 bit)

getting a coin flip

int seed = 0;int randomNumber = 0;

cout << "type a number to seed generator";cin >> seed;srand( seed );randomNumber = rand( )%2; // 0 or 1

#include <ctime>• time( 0 ); - returns the number of seconds

since Jan 1 1970. I have no idea why. But, not an integer, some mutant "time" string…

• so:#include <ctime>#include <cstdlib>

srand ( (int) time(0) ); // seed random number generator with time

actually, time(0) is a "structure"

• a structure, or "struct" in C++, is a meta-variable, that contains many variables… one main, and a number of auxiliary values

• the "time" struct contains the number of seconds (its main value), but also month, day, date and year which we can access when we get good at this

#include <iostream>#include <string >#include <math.h>#include <cstdlib>#include <ctime>using namespace std;

int main( ) {

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Design

1. Flip some coins: a lot of them, in a for loop- use rand to generate numbers 0-9.- 0-4 are heads, 5-9 are tails

2. Count the number of heads and the number of tails

Design

3. abs(heads - tails) / 2 is the number of errant coin flipse.g. For 10 flips, if you get 6 heads and 4 tails, 6 - 4 / 2 = 1 coin flip was errant

NOTE THAT THIS INVOLVES DIVIDING INTEGERS

we will use Casting

ints and doubles ARE interchangeable but we have to cast

int x;double y;

x = 10;y = (double)x;

casting

int numberOfFlips=0;int numberOfHeads=0; int numberOfTails=0;int diff = 0; // mistakedouble percentage = 0.0;

diff = abs( numberOfHeads - numberOfTails )/2;// no division should EVER be done with integers

best: all divisions done with doubles

double diff = 0.0;diff = (double) (abs( numberOfHeads - numberOfTails )) /2.0;

4. Calculate total % of errant flipspercentage =

(diff/(double)(numberOfFlips)) * 100.0;

Design5. Finally, is percentage greater

than 10%?- stay home