Stack around the variable ' ' is corrupted , c++ issue - c++

Question

I got a little problem about this program i am making ,
The main purpose of this program I am making is to get 2 polynomial and sum / sub / multiply it ,
Didn't finished the output and main() parts yet, just on the code itself,
When I try to use the multiply part,
I get this error : stack around the variable 'a' is corrupted ,
Dunno what I did wrong .... took me 1 hours to think of this way and write this , but just 2 hours trying to fix this but can't get anywhere.
class PolyNomial
{
int printcounter;
double *coefficients;
int degree;
public:
PolyNomial()//the default constructor to initialize a polynomial equal to 0
{
degree = 0;
coefficients = new double[degree + 1];
coefficients[0] = 0;
}
PolyNomial(double y[], int x)//the constructor to initialize a polynomial with the given coefficient array and degree
{
degree = x;
if (degree>10)
{
cout<<"Error : The PolyNomial's Degree is bigger than 10 and can not be shown in this program";
}
else
{
int c=0;
coefficients = new double[degree + 1];
for(c=0;c<=degree;c++)
{
coefficients[c] = y[c];
}
}
}
void add(PolyNomial p)
{
int i;
if ( degree < p.degree )
{
i = p.degree;
printcounter = p.degree;
}
else
{
i = degree;
printcounter = degree;
}
for(;i>=0;i--)
{
coefficients[i] = coefficients[i] + p.coefficients[i];
}
}
void sub(PolyNomial p)
{
int i;
if ( degree < p.degree )
{
i = p.degree;
printcounter = p.degree;
}
else
{
i = degree;
printcounter = degree;
}
for(;i>=0;i--)
{
coefficients[i] = coefficients[i] - p.coefficients[i];
}
}
void print()
{
int i;
for(i=0;i<=printcounter;i++)
cout<<coefficients[i]<<" ";
}
void Multiply(PolyNomial p)
{
int i,j;
i = degree;
j = p.degree;
double a[100];
int counter;
for ( counter = 0 ; counter <= i+j; counter++)
{
a[counter]=0;
}
int x= i+ j ;
for(;i>=0;i--)
{
for(;j>=0;j--)
if (i+j>=10)
{
cout<<"Error : The PolyNomial's Degree is bigger than 10 and can not be shown in this program";
break;
}
a[i+j] = a[i+j] + ( coefficients[i] * p.coefficients[j] );
}
PolyNomial k(coefficients,x);
k.print();
}
};
int main()
{
double a[100];
int x,i;
cout<<"Enter the PolyNomial's Degree : ";
cin>>x;
cout<<"\nEnter the coefficients one by one by , from bigger to smaller : ";
for ( i=0 ; i<=x ; i++ )
{
cin>>a[i];
}
PolyNomial p(a,x);
cout<<"\n\nEnter the PolyNomial's Degree : ";
cin>>x;
cout<<"\nEnter the coefficients one by one by , from lowest degree to highest : ";
for ( i=0 ; i<=x ; i++ )
{
cin>>a[i];
}
PolyNomial o(a,x);
_getch();
// p.add(o);
p.Multiply(o);
// p.print();
_getch();
// p.sub(o);
// p.Multiply(o);
}

Answer 1

This line
a[i+j] = a[i+j] + ( coefficients[i] * p.coefficients[j] );
is not inside the for j loop (you haven't used { and } to enclose it}. This means that j is -1 when it gets run. If i is 0 you are assigning to a[-1] which causes the stack corruption message.
Note that you also aren't resetting j each time round the i loop, so the inner loop will only execute once.

Answer 2

In C and C++ local variables are generally stored on the stack, a small(ish) area of memory that programs use to store local/function level data; when an executable calls a function, the processor uses the stack to store the address that the call is being made from, and then branches to the subroutine. When the subroutine finishes, if it has cleaned up it's stack, then it should be back to a state where the top value of the stack is the address it needs to jump back to in order to resume processing.
At the same time, C/C++ programs use the stack to store local variables -- the principle being that when you leave a sub-routine all the variables go away very elegantly.
Your variables "a" are local variables, they are on the stack. Since they are arrays, that means that if you write outside the contraints of the array, you will overwrite areas of the stack being used by other variables or possibly even by the CPU for return-address tracking.
Your variables "a" have 100 elements. This array forms a single, contiguous block:
{a[0]}{a[1]}...{a[99]}
If you write to 'a[100]' you are writing past the end of the array and over some other variable's memory, or possibly the return address of a function.
You might want to consider using a [std::array][1] or a [std::vector][2].

Answer 3

At the time you create your polynomial, you create a coefficients array with the size of degree + 1. So far so good. Now if you add two polynomials, you simply add the coefficients but disregard the allocated space. If the polynomial with the lowest degree should be the result of the addition, you'll get in trouble

Answer 4

Well for now tnx to all the answers and comments i got my code working but it dose not do the job correctly,
Example : if I add a 2 degree polynomial first then a 3 degree like this :
1 2 3
1 2 3 4
The result will be :
0 0 3 6 9 12
Which is only one part of the multiply processes,
The 2 polynomial I added are :
3x^2 + 2x^1 + 1
4x^3 + 3x^2 + 2x^1 + 1
Here is the new code :
class PolyNomial
{
int printcounter;
double *coefficients;
int degree;
public:
PolyNomial()//the default constructor to initialize a polynomial equal to 0
{
degree = 0;
coefficients = new double[degree + 1];
coefficients[0] = 0;
}
PolyNomial(double y[], int x)//the constructor to initialize a polynomial with the given coefficient array and degree
{
degree = x;
if (degree>10)
{
cout<<"Error : The PolyNomial's Degree is bigger than 10 and can not be shown in this program";
}
else
{
int c=0;
coefficients = new double[degree + 1];
for(c=0;c<=degree;c++)
{
coefficients[c] = y[c];
}
}
}
void add(PolyNomial p)
{
int i;
if ( degree < p.degree )
{
i = p.degree;
printcounter = p.degree;
}
else
{
i = degree;
printcounter = degree;
}
for(;i>=0;i--)
{
coefficients[i] = coefficients[i] + p.coefficients[i];
}
}
void sub(PolyNomial p)
{
int i;
if ( degree < p.degree )
{
i = p.degree;
printcounter = p.degree;
}
else
{
i = degree;
printcounter = degree;
}
for(;i>=0;i--)
{
coefficients[i] = coefficients[i] - p.coefficients[i];
}
}
void print()
{
int i;
for(i=0;i<=printcounter;i++)
cout<<coefficients[i]<<" ";
}
void Multiply(PolyNomial p)
{
int i,j;
i = degree;
j = p.degree;
double mult[100];
int counter;
for ( counter = 0 ; counter <= i+j; counter++)
{
mult[counter]=0;
}
int x= i+ j ;
for(;i>=0;i--)
{
for(;j>=0;j--)
{
if (i+j>=10)
{
cout<<"Error : The PolyNomial's Degree is bigger than 10 and can not be shown in this program";
break;
}
mult[i+j] = mult[i+j] + ( coefficients[i] * p.coefficients[j] );
}
}
PolyNomial k(mult,x);
k.printcounter = x;
k.print();
}
};
int main()
{
double a[100];
int x,i;
cout<<"Enter the PolyNomial's Degree : ";
cin>>x;
cout<<"\nEnter the coefficients one by one by , from lowesr degree to highest : ";
for ( i=0 ; i<=x ; i++ )
{
cin>>a[i];
}
PolyNomial p(a,x);
cout<<"\n\nEnter the PolyNomial's Degree : ";
cin>>x;
cout<<"\nEnter the coefficients one by one by , from lowest degree to highest : ";
for ( i=0 ; i<=x ; i++ )
{
cin>>a[i];
}
PolyNomial o(a,x);
_getch();
// p.add(o);
p.Multiply(o);
// p.print();
_getch();
// p.sub(o);
// p.Multiply(o);
}