Not able to figure out what is happening with the universal array - c++

Question

I have created a program which takes an equation. from the user by asking about the degree of the equation. and then taking the co-efficients from the user and then forming the function which results into an equation. and then I have used the bisection method to solve it.
The program is::
#include<iostream>
#include<math.h>
#include<iomanip>
using namespace std;
int stop=0,d,t[]={1};
float f(float x)
{
int loop,loopa;
float add=0.0,sum=0.0;
for(;stop==0;)
{
int p ;
cout << "Enter the degree of the poly. eq. (+ve integer)" << endl;
cin >> d ;
int *t = new int[d+1];
cout << "The eq. will be in the form of ax^"<<d<<"+bx^"<<(d-1)<<" and so on ." ;
p = 97 + d ;
for(loop=d;loop>=0;loop--)
{
cout << "Enter the value of " << char(p-loop) << endl;
cin >> t[loop];
cout << "a="<<t[loop]<<endl;
}
stop=1; //ARRAY IS STILL THERE WHY/////
} for(loop=0;loop<=d;loop++) cout<<"out="<<t[loop]<<endl;
//ARRAY IS GONE TILL NOW//
cout<<"d="<<d<<endl;
for(loopa=d;loopa>=0;loopa--)
{
cout<<"loopa="<<loopa<<"value="<<t[loopa]<<endl;
add = t[loopa] * pow(x,loopa);
sum=sum+add;
}
return sum;
}
int main()
{
float a , b , c , i , j ;
A:
cout << " Enter the starting point of interval " <<endl;
cin >> a ;
cout << " Enter the end point of interval " << endl;
cin >> b ;
cout << " Enter the number of iterations to be done . ( More the iterations , accurate is the result ) " << endl;
cin >> i ;
for(j=0;j<i;j++)
{
if(f(a)*f(b)>0)
{
cout << " The root of the above polynomial does not lies in the given interval . TRY AGAIN " << endl;
goto A;
}
else
{
c = a + b ;
c = c / 2 ;
if (f(a)*f(c)>0) a = c ;
else b = c ;
cout <<"hello"<< a << "aa \t" << b << "\t" << c << endl;
}
}
cout << "Root = "<< c <<endl;
}
When the user gives the value of degree it creates an array of size one more than degree is created then there is a for loop which takes the value of co-efficients in that array . The problem is the value of the array stays intact till the first for loop . but as the control proceeds to the second loop ( see the two comments ) the value of the array is gone...I am using CodeLite ...guys help me?????

Answer 1

To solve the array issue you just need to make a few small changes.
int stop=0,d,*t; // Declare an uninitialized pointer to int
float f(float x)
{
int loop,loopa;
float add=0.0,sum=0.0;
for(;stop==0;)
{
int p ;
cout << "Enter the degree of the poly. eq. (+ve integer)" << endl;
cin >> d ;
t = new int[d+1]; // Remove the int and asterix before t. You want to assign the new array to the pointer, not the value the pointer is pointing to.
cout << "The eq. will be in the form of ax^"<<d<<"+bx^"<<(d-1)<<" and so on ." ;
p = 97 + d ;
for(loop=d;loop>=0;loop--)
{
cout << "Enter the value of " << char(p-loop) << endl;
cin >> t[loop];
cout << "a="<<t[loop]<<endl;
}
stop=1; //ARRAY IS STILL THERE WHY/////
} for(loop=0;loop<=d;loop++) cout<<"out="<<t[loop]<<endl;
//ARRAY IS GONE TILL NOW//
cout<<"d="<<d<<endl;
for(loopa=d;loopa>=0;loopa--)
{
cout<<"loopa="<<loopa<<"value="<<t[loopa]<<endl;
add = t[loopa] * pow(x,loopa);
sum=sum+add;
}
delete[] t; // All new'ed things need to be deleted to not cause a leak. Delete it here since it is no longer needed.
return sum;
}
Please note that even if this works, it is not advised to use raw pointers in C++. Better to use an std::array<int> or std::vector<int> so you don't have to take care of the allocating and deleting of memory.
EDIT: Accidentaly left the int in fron of t. Changed now.