Question

NEED HELP IN C++, IT'S UGENT. I been trying to figure out for hours what is wrong with my code. I can not get the first derivative to display and its evaluation to display. my code is below:

#include <iostream>
#include <cmath>
#include <iomanip>
#include <string>
#include <sstream>
using namespace std;

string polyToString(double poly[])
{

stringstream ss;

if (poly[0] == 0)
{
ss << poly[1];
}
  
if (poly[0] == 1)
{
int a = poly[1];
int b = poly[2];
  
if (b > 0)
{
if (a == 1)
ss << "x + " << b;
else if (a == -1)
ss << "-x + " << b;
else
ss << a << "x + " << b;
}
else if (b < 0)
{
if (a == 1)
ss << "x " << b;
else if (a == -1)
ss << "-x " << b;
else
ss << a << "x " << b;
}
else
if (a == 1)
ss << "x";
else if (a == -1)
ss << "-x";
else
ss << a << "x";
}
  
if (poly[0] > 1)
{
int degree = poly[0];
int i;
if (poly[1] == 1)
ss << "x^" << degree;
else if (poly[1] == -1)
ss << "-x^" << degree;
else
ss << poly[1] << "x^" << degree << " ";
for (i = 2; i <= degree-1; i++)
{
if (poly[i] > 0)
{
if (poly[i] == 1)
ss << " + " << "x^" << degree - i+1 << " ";
else if (poly[i] == -1)
ss << " + " << "-x^" << degree - i+1 << " ";
else
ss << " + " << poly[i] << "x^" << degree - i+1 << " ";   
}
else if (poly[i] < 0)
{
if (poly[i] == 1)
ss << " - " << "x^" << degree - i+1 << " ";
else if (poly[i] == -1)
ss << " - " << "-x^" << degree - i+1 << " ";
else
ss << " - " << poly[i] << "x^" << degree - i+1 << " ";   
}
else
;
}
  
  
int a = poly[i];
int b = poly[i + 1];
  
if (b > 0)
{
if (a > 0)
{
if (a == 1)
ss << "+ x + " << b;
else
ss << "+ " << a << "x + " << b;
}
else if (a < 0)
{
if (a == -1)
ss << "- x + " << b;
else
ss << a << "x + " << b;
}
else
ss << "+ " << b;
}
else if (b < 0)
{
{
if (a > 0)
{
if (a == 1)
ss << "+ x +- " << b;
else
ss << "+ " << a << "x - " << b;
}
else if (a < 0)
{
if (a == -1)
ss << "- x - " << b;
else
ss << "- " << a << "x - " << b;
}
else
ss << b;
}
}
else
if (a > 0)
{
if (a == 1)
ss << "+ x";
else
ss <<"+"<< a << "x";
}
else if (a < 0)
{
if (a == -1)
ss << "- x";
else
ss << a << "x";
}
else
;
  
}
  
return ss.str();
  
}

double polyEval(double poly[],double x)
{
int degree = poly[0];
double result = 0;
int n = 1;
int i;

for (i=degree; i > 0; i--)
{
result += poly[i]*(pow(x,n));
n++;
}

result += poly[degree+1];

return result;

}

double* differentiate(double poly[])
{
int degree = poly[0];

double *result = new double[degree+1];
*result = degree-1;
int n = degree;
int i;
for (i = 1; i <= degree; i++)
{
result[i] = poly[i]*n;
n--;
}

return result;
delete[] result;
}

int main()
{
cout << "Enter the degree of the polynomial -> ";
int degree;
cin >> degree;
int size = degree+1;
cout << "Enter the coefficients -> ";
double *poly = new double[size+1];
*poly = degree;
int i;
for (i = 1; i <= size; i++)
{
cin >> poly[i];
}

cout << "f(x) = " << polyToString(poly) << endl<< endl;

cout << "Enter a value at which to evaluate this polynomial -> ";
double x;
cin >> x;

cout << "f(" << x << ") = " <<setprecision(6)<< polyEval(poly,x)<< endl<< endl;

double* oneprime = NULL;
oneprime = differentiate(poly);
cout << "f’(x) = " << polyToString(oneprime) << endl;
  
cout << "Enter a value at which to evaluate this polynomial -> ";
double y;
cin >> y;
cout<< "f'("<<y<<")="<< polyEval(oneprime,y)<< endl;

double* twoprime= NULL;
twoprime = differentiate(oneprime);
cout<<"f\"(x) = "<< polyToString(twoprime) << endl;
cout<< "Enter a value at which to evaluate this polynomial - > ";
double z;
cin>> z;
cout<<"f\"("<<z<<")= "<< polyEval(twoprime,z)<<endl;

return 0;
}

Answer 1

Hi,

Your code is completely correct. You might be using gcc compiler which might have caused the issue.

Use g++ compiler to compiler C++ source code instead of gcc.

I have given the output from your program for your reference.

It would be real help for me if you please rate my answer.