C++ Stack Overflow Error

Question

Am trying to get myself used to working with dynamic arrays in c++ and now am stuck for like the tenth time today. The program compiles fine, but after taking inputs it gives the stack overflow error, and I have provided functionality to delete the heap in my constructor, I assumed I had an uninitiated variable but i really cant find it. Am hoping you guys can help me check it out. This is the code:

#include<string>
#include<cmath>
#include<sstream>
using namespace std;
#include"Calc.h"
#include<iostream>
using namespace std;

Calc::Calc(int a, int*b){
length=a;
ar=b;
AR =new int*[length];


for (int i=0; i<length;i++){
    AR[i] = new int [ar[i]]();
    }

for (int i = 0; i < length; i++)
    delete[] AR[i];
    };

Calc::~Calc(){};

int Calc::solveFor(int m0, int n0){
int ans=0;
if (m0=0) {ans =n0+1; AR[m0][n0]=ans; return n0+1;}
if (n0=0) {ans= solveFor(m0-1,1); AR[m0][n0]=ans;return ans;}
else {ans=solveFor(m0-1, solveFor(m0, n0-1));AR[m0][n0]=ans; return ans;}
};



void Calc::getSolved(){
for(int i=0; i<=length; i++){cout<<endl;
    for (int j=0; j<ar[i]; j++)
        cout<<"ACK ["<<i<<","<<j<<"]="<<AR[i][j]<<"  ";}
    cout<<endl;


};

The Run.cpp:

#include<iostream>
#include<string>
#include "Calc.h"

using namespace std;

int main() {
int m;
int n;
int v[6]= {7, 7, 7, 7, 7, 7};
Calc XXX(6, v);
cin>>m;
cin>>n;


XXX.solveFor(m,n);
XXX.getSolved();

  return 0;
}

thanks in advance.

Your constructor shouldn't immediately free the memory it allocated. Move the delete loop to the destructor. — molbdnilo
– molbdnilo, Commented Oct 24, 2012 at 6:08

codaddict · Accepted Answer · 2012-10-24 05:08:56Z

3

One issue I can see in Calc::solveFor is you are using the assignment operator in place of equality:

if (m0=0)

should be

if (m0==0)

answered Oct 24, 2012 at 5:08

codaddict

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Comments

user434817 · Accepted Answer · 2012-10-24 05:13:07Z

1

Apart from the =/== problem mentioned above, it looks like you are calculating the Ackermann function recursively. The recursion depth of this function grows way too fast to do it this way: "A(4, 2) cannot possibly be computed by simple recursive application of the Ackermann function in any tractable amount of time."

Try an iterative approach instead, or have a look at memoization.

answered Oct 24, 2012 at 5:13

user434817

2 Comments

John Manson Over a year ago

the iterative approach seemed too bulky, but if its my only choice i will give it a try

user434817 Over a year ago

The Ackermann function works very nice with memoization. Use a 2-dimensional array of pre-calculated function values, initialize with a token value, say -1, and everytime the function is called, check if the value for the current parameters (== array position) has already been calculated before. If so, just use that value. If not, calculate and store the return value in the array. That way, you save lots of recursions, no more stack overflow, the code runs MUCH faster, and you can stay with the recursive approach...

Andriy · Accepted Answer · 2012-10-24 06:43:06Z

0

The value of the Ackermann function grows very rapidly, and for m>3 it would overflow int which you use for the result. That may be the reason for the infinite recursion.

answered Oct 24, 2012 at 6:43

Andriy

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