Thread: logic Error

with this program i am supposed to use a vector to store the numbers of times each possible sum of the two dice appears. I am rolling the dice 36000 times. The vector contains 11 element from 2 to 12. could you tell me why i am not getting reasonable results. i am getting a very huge number for case 12..

Code:

#include<iostream>
using namespace std;

#include<vector>
using std::vector;

#include<cstdlib>
using std::rand;
using std::srand;

#include<ctime>
using std::time;

#include<iomanip>
using std::setw;

int SumOfDice;
vector<int>Frequency(11);
int x;
int y;

int main()
{
int sumOfDice;
vector<int>Frequency(11);
int x;
int y;
srand(time(0));


for( int i=1; i<=36000; i ++)
{
x = 1+rand()%6;
y =1 +rand()%6;

SumOfDice = x+y;


switch (SumOfDice)
{
case 2:
Frequency[SumOfDice]++;
break;

case 3:
Frequency[SumOfDice]++;
break;

case 4:
Frequency[SumOfDice]++;
break;

case 5:
 Frequency[SumOfDice]++;
break;

case 6:
Frequency[SumOfDice]++;
break;

case 7:
Frequency[SumOfDice]++;
break;

case 8:
Frequency[SumOfDice]++;
break;

case 9:
Frequency[SumOfDice]++;
break;

case 10:
Frequency[SumOfDice]++;
break;

case 11:
Frequency[SumOfDice]++;
break;

case 12:
Frequency[SumOfDice]++;
break;


 default :
 cout<<"incorrect number"<<endl;
break;

}
}
cout<<"Frequency"<<setw(50)<<"number of times each sum appears"<<endl;
for( int i = 2;i<=12;i++)
cout<<i<<setw(50)<<Frequency[i]<<endl;

return 0;
}
//the output is
Frequency                  number of times each sum appears
2                                              1017
3                                              2024
4                                              2939
5                                              4104
6                                              5023
7                                              6066
8                                              4993
9                                              3855
10                                              3020
11                                              1993
12                                         134523750

You're reading (and writing) beyond the end of the vector. You allocated a vector of size 11. That's Frequency[0] - Frequency[10], but you're using Frequency[2] - Frequency[12].

EDIT: opps, beat me to....gee, my internet connection isn't that slow, surely

As it is, it *looks* like your display function is trying to call beyond what it exists, thus the large reading. Change your vector to 13, should fix that ?

Code:

int SumOfDice;
vector<int>Frequency(11);
int x;
int y;

int main()
{
   int sumOfDice;

However descriptive, naming variables where the only difference is caps can lead to unnecessary bugs and dificulty reading.

Code:

x = 1+rand()%6;
y =1 +rand()%6;

SumOfDice = x+y;

=?

Code:

x = rand()%6;
y = rand()%6;

SumOfDice = x+y+2;