cout << probability[n][n];
probability[][]
is an n by n array. The last element is probability[n-1][n-1]
, so you are running off the end of the array and invoking undefined behavior.
Вопрос
I'm compiling this on linux. It will compile and run, but when I enter values for n and p, this is what my terminal looks like:
7 1.0 Segmentation fault (core dumped)
In this case, 7 is the input for n, and 1.0 is the input for p. I've tried this with different values. The idea is to use Dynamic Programming to fill in a 2D array of probabilities through recursion. Let me know if you need more info, but this is the entirety of the code.
#include <iostream>
using namespace std;
int main(int argc, char *argv[])
{
int n;
double p;
cin >> n;
cin >> p;
cout << n;
cout << p;
cout << "Initializing array.";
double** probability = new double*[n];
for(int i = 0; i < n; ++i)
{
probability[i] = new double[n];
}
//cout << "Beginning filling i loop.";
for(int i = 0; i < n; i++)
{
probability[i][0] = 0;
}
//cout << "Beginning filling j loop.";
for(int j = 0; j < n; j++)
{
probability[0][j] = 1;
}
//cout << "Beginning filling nested loop.";
for(int i = 1; i< n; i++)
{
for(int j = 1; j< n; j++)
{
probability[i][j] = (p * probability[i-1][j]) + ((1-p) * probability[i][j-1]);
}
}
cout << "Probability: ";
cout << probability[n][n];
//cleanup
for(int i = 0; i < n; ++i)
{
delete probability[i] ;
}
delete probability;
return 0;
}
Решение
cout << probability[n][n];
probability[][]
is an n by n array. The last element is probability[n-1][n-1]
, so you are running off the end of the array and invoking undefined behavior.