So I've made a basic polynomial class in C++ which stores the coefficients of these polynomials dynamically on the heap. I'm currently in the process of overloading operators so that I can add/subtract polynomials together in order to simplify them etc.
However I'm getting unexpected results when I try to overload the * operator. It looks like instead of returning the value of an index in the array it is returning the position of the array.
This is my *operator method in my .cpp file:
Polynomial Polynomial::operator*(Polynomial p) {
int maxDegree = (degree)+(p.degree - 1);
int *intArray3 = new int[maxDegree];
int i, j;
for (int i = 0; i < degree; i++) {
for (int j = 0; j < p.degree; j++) {
cout << getCoef(i) << " * " << p.getCoef(j) << " = " << getCoef(i)*p.getCoef(j) << endl;
intArray3[j] += (getCoef(i))*(p.getCoef(j));
cout << " intArray3[" << j << "] contains : " << intArray3[j] << endl;
}
}
return Polynomial(maxDegree, intArray3);}
The lines:
cout << getCoef(i) << " * " << p.getCoef(j) << " = " << getCoef(i)*p.getCoef(j) << endl;
and
cout << " intArray3[" << j << "] contains : " << intArray3[j] << endl;
return
10 * 1 = 10
intArray3[0] contains : -842150441
in my console. I'm assuming that the problem lies with my use of pointers somewhere but I can't for the life of me think why. I implemented this overload in a similar way to my + and - overloads and they work fine. Any assistance would be greatly appreciated. Cheers.
Related
So I'm working on this project where I have to gather 2 integers from a user 3 times (loop), and each time I have to print the two integers in ascending order. The restriction is that you can only have two cout statements within your loop (one is asking for their input and the second is outputting the ascending order).
My only issue with that is, when I think about ascending order, I would do it like (which has two count statements):
if (m<n) {
cout << m << n << endl;
if (m>n){
cout << n << m << endl;
So far, this is what I have:
#include <iostream>
using namespace std;
int main(int,char**) {
int n, m, z;
for (n=0;n<3;n++){
cout << "Give me two numbers: ";
cin >> m;
cin >> z;
//if (m>z);
//cout << m << z << "sorted is: " << m << z << endl;
// This is where I'm getting stuck because I need two count statements to organize in ascending order as shown above
}
}
So have you considered to change which variable holds the lower number? e.g.
if(m > n){
int temp = n;
n = m;
m = temp;
}
Then you can just use one print
cout << m << " " << n << endl;
This is where I'm getting stuck because I need two count[sic]
statements to organize in ascending order as shown above
You have marked this post as C++:
Additional options to consider:
use algorithm lib:
#include <algorithm>
std::cout << std::min(m,n) << " " << std::max(m,n) << std::endl;
or use conditional / ternary operator in your cout:
std::cout << ((m<n) ? m : n) << " " << ((n<m) ? m : n) << std::endl;
References are sometimes fun ... but perhaps this challenge is too trivial.
// guess m < n
int& first = m;
int& second = n;
if(!(m<n)) { first = n; second = m; }
std::cout << first << " " << second << std::endl;
Pointers can do the same:
// guess m < n
int& first = &m;
int& second = &n;
if(!(m<n)) { first = &n; second = &m; }
std::cout << *first << " " << *second << std::endl;
or you can use
lambda expressions, or
c++ functions, or
c++ class methods
But I think each of these would be directly comparable to either of the first alternatives.
Here's the code:
#include "stdafx.h"
#include <iostream>
using namespace std;
int main()
{
int keyArray[7] = {1,2,3,4,5,6,7};
int breakPoint;
int counter;
for (counter = 0; counter < 7; counter++)
{
// keyArray[counter] = (rand() % 9) + 1; later
keyArray[counter] = counter; //testing
}
cout << keyArray[0] + "\n";
cout << keyArray[1] + "\n";
cout << keyArray[2] + "\n";
cout << keyArray[3] + "\n";
cout << keyArray[4] + "\n";
cout << keyArray[5] + "\n";
cout << keyArray[6] + "\n";
cin >> breakPoint; //so I can see what the hell is going on before it disappears
return 0;
}
The only reason I gave values to keyArray was that I read in answer to a similar question that you have to initialize an array with data before you use it. But it made no difference. The output is just junk symbols whether you initialize or not.
The compiler is Visual Studio Community 2017. Thanks for any help.
The error is not in your logic but rather in your debugging output. Since the other answers focus on how to fix it, I'll rather explain what happens instead. There seems to be a misunderstanding about the way strings work in C++.
The failure is in this operation:
keyArray[0] + "\n"
Internally, string literals are arrays of characters, in this case const char[2], consisting of the newline and a terminating '\0' null terminator. When you then try to add the integer and this array together, the array will be represented by a pointer to its first element, i.e. it will decay to const char* in order to be used as the second argument to the plus operator used in your code.
So for the compiler, this line will need operator+(int, const char*). But the result of that will be const char*, the input pointer offset by the integer, as that is the operation that happens when adding integers to pointers.
So instead of printing the number and then the string, it will try to access a string that does not exist as the pointer now pointer behind the string "\n" and thus into some arbitrary memory.
Instead of doing
cout << keyArray[0] + "\n"
do:
cout << keyArray[0] << "\n"
or
cout << keyArray[0] << endl
You can't concatanate an integer with a string. That's why you got garbage output
Try this first:
cout << keyArray[0] << "\n";
If you are using compilers that support C++ 11 then try using std::to_string(...) to make a string from an integer before doing the addition:
cout << (std::to_string(keyArray[0]) + "\n");
you cannot concatenate int with string.
change
cout << keyArray[0] + "\n";
cout << keyArray[1] + "\n";
cout << keyArray[2] + "\n";
cout << keyArray[3] + "\n";
cout << keyArray[4] + "\n";
cout << keyArray[5] + "\n";
cout << keyArray[6] + "\n";
to
cout << keyArray[0] << "\n"
<< keyArray[1] << "\n"
<< keyArray[2] << "\n"
<< keyArray[3] << "\n"
<< keyArray[4] << "\n"
<< keyArray[5] << "\n"
<< keyArray[6] << endl;
You need to convert the integers into a string. Using a relatively recent version of C++:
#include "stdafx.h"
#include <iostream>
using namespace std;
int main()
{
int keyArray[7] = {1,2,3,4,5,6,7};
int breakPoint;
int counter;
for (counter = 0; counter < 7; counter++)
{
// keyArray[counter] = (rand() % 9) + 1; later
keyArray[counter] = counter; //testing
}
cout << std::to_string(keyArray[0]) + "\n";
cout << std::to_string(keyArray[1]) + "\n";
cout << std::to_string(keyArray[2]) + "\n";
cout << std::to_string(keyArray[3]) + "\n";
cout << std::to_string(keyArray[4]) + "\n";
cout << std::to_string(keyArray[5]) + "\n";
cout << std::to_string(keyArray[6]) + "\n";
cin >> breakPoint; //so I can see what the hell is going on before it disappears
return 0;
}
I'm having trouble getting the size of a vector by dot-walking from a parent vector into the one in question. I have verified that calling the function myfunc 1 2 3 4 5 creates five Person objects and puts them in the left vector. But when I try to get that same size to return by dot-walking from bridge to left, I get 0 as the size.
What am I doing wrong?
int main(int argc, char* argv[]) {
Person* p_ptr;
int id_source = 0;
vector<Person> left;
vector<Person> right;
bridge.push_back(left);
bridge.push_back(right);
cout << "bridge.size() = " << bridge.size() << endl;
for (int i = 1; i < argc; i++) {
id_source++;
cout << "Creating Person with crossing speed of " << argv[i] << " and id of " << id_source << endl;
p_ptr = new Person(atoi(argv[i]), id_source);
left.push_back(*p_ptr);
}
/*SIZE TESTING*/
cout << "Left side of bridge has " << left.size() << " people on it " << endl;
cout << "bridge.at(0).size() = " << bridge.at(0).size() << endl;
cout << "bridge.at(1).size() = " << bridge.at(1).size() << endl;
int slowest_id = get_slowest(0);
for (int i = 0; i < left.size(); i++) {
if (slowest_id == left.at(i).get_id()) {
p_ptr = &left.at(i);
}
}
cout << "The slowest person has id of " << slowest_id << " and speed of " << p_ptr->get_crossing_time() << endl;
}
}
left and bridge[0] are two different lists. When you call bridge.push_back(left) you make a copy of the current left list (which is empty). Elements added later will not be in the bridge version.
I'm working with flann library with point clouds. I have this adapter method that transform my own points to a flann-usable points
flann::Matrix<float> * converterFlann::convertArray(vector<Point *> *P){
float points[P->size()*3];
int j = 0;
for (int i = 0; i<P->size(); i++){
points[j] = P->at(i)->getX(); j++;
points[j] = P->at(i)->getY(); j++;
points[j] = P->at(i)->getZ(); j++;
}
P->at(0)->print();
cout << points[0] << " " << points[1] << " " << points[2] << endl;
flann::Matrix<float> *nari = new flann::Matrix<float>(points, P->size(), 3);
cout << *nari[0][0] << " " << *nari[0][1] << " " << *nari[0][2] << endl;
return nari;
}
And the output of this method is
Printing my point: (-0.06325, 0.0359793, 0.0420873) Index: 0
Printing from points array: -0.06325 0.0359793 0.0420873
Printing from flann: -0.06325 -0.06275 -0.0645
I don't understand why printing from flann::Matrix, Y and Z are different. I've been looking for some documentation about storing procedure of flann::Matrix but I'm not able to find any answer. I thing that my array-type access is correct but it doesn't work.
Thanks in advance. :D
I'm having a problem where the objects in my array are lost when I pass the array through a constructor. My first guess was that I needed to change it to an array of pointers but that resulted in a segfault. My next guess was that I needed to copy the array data after passing it but that also didn't work. Here's the problem code:
Universe Object:
class Universe {
public:
Star stars[]; int starsLength;
Planet planets[]; int planetsLength;
public:
Universe(Star st[], int stl, Planet pl[], int pll) {
stars < st; starsLength = stl;
planets < pl; planetsLength = pll;
}
Universe() {
}
public:
void render() {
for(int i = 0;i < starsLength;i++) {
//std::cout << "STAR: " << stars[i].location.x << "," << stars[i].location.y << " " << stars[i].size << " " << stars[i].color.r << "," << stars[i].color.g << "," << stars[i].color.b << "\n";
renderCircle(stars[i].location, stars[i].size, stars[i].color);
}
for(int i = 0;i < planetsLength;i++) {
renderCircle(planets[i].location, planets[i].size, planets[i].color);
}
}
void renderCircle(Point location, float size, Color color) {
glBegin(GL_LINES);
glColor3f(color.r,color.g,color.b);
glVertex2f(location.x+size, location.y+size);
glVertex2f(location.x-size, location.y-size);
glVertex2f(location.x-size, location.y+size);
glVertex2f(location.x+size, location.y-size);
glEnd();
}
};
Method that creates the Universe and gives it the array:
Universe buildUniverse(int size, int seed) {
Point bounds = Point{static_cast <float> (size),static_cast <float> (size)}; //0,0 to size,size
int starCount = min(size/10,random(size/5));
int planetCount = min(size/3,random(size));
Star stars[starCount];
Planet planets[planetCount];
//std::cout << "-- Created " << starCount << " stars and " << planetCount << " planets...\n";
for(int i = 0;i < starCount;i++) {
Point location = {random(bounds.x),random(bounds.y)};
Point velocity = {random(bounds.x/100.0f),random(bounds.y/100.0f)};
float size = random(bounds.x/100.0f);
float mass = random(size*(random(1.0f)+0.5f));
Color color = {1.0f,1.0f,1.0f};
stars[i].setStar(location,velocity,size,mass,color);
}
for(int i = 0;i < planetCount;i++) {
Point location = {random(bounds.x),random(bounds.y)};
Point velocity = {random(bounds.x/100.0f),random(bounds.y/100.0f)};
float size = random(bounds.x/100.0f);
float mass = random(size*(random(1.0f)+0.5f));
Color color = {random(1.0f),random(1.0f),random(1.0f)};
planets[i].setPlanet(location,velocity,size,mass,color);
}
Universe uni = {stars, starCount, planets, planetCount};
std::cout << "Star in array: " << stars[0].location.x << "," << stars[0].location.y << " " << stars[0].size << " " << stars[0].color.r << "," << stars[0].color.g << "," << stars[0].color.b << "\n";
std::cout << "Star passed to uni in an array: " << uni.stars[0].location.x << "," << uni.stars[0].location.y << " " << uni.stars[0].size << " " << uni.stars[0].color.r << "," << uni.stars[0].color.g << "," << uni.stars[0].color.b << "\n";
return uni;
}
Output of of the program:
Building universe...
Star in array: 39.922,39.155 0.167611 1,1,8.85715e-39
Star passed to uni in an array: 7.00649e-45,2.24208e-44 0.0282954 5.90446e-39,1.4013e-45,1.4013e-45
Initializing threaded renderer...
Starting simulation...
What am I doing wrong?
First, your code is not valid C++. Declaring empty arrays using [] does not exist in C++.
So the first thing is to turn this into valid C++ that still preserves what you're trying to accomplish. One solution is to use std::vector:
#include <vector>
class Universe {
public:
std::vector<Star> stars;
std::vector<Planet> planets;
public:
Universe(const std::vector<Star>& st,
const std::vector<Planet>& pl) : stars(st), planets(pl) {}
};
Note the replacement of the non-C++ code with std::vector. Also note that we initialize the vectors using the initializer-list.
Last, note that we no longer need to keep the sizes as separate member variables. Why? Because a vector knows its size by calling the vector::size() member function. For example:
for(int i = 0;i < starsLength;i++) {
can be replaced with
for(int i = 0;i < stars.size();i++) {
In your buildUniverse function, use the following changes:
Universe buildUniverse(int size, int seed) {
Point bounds = Point{static_cast <float> (size),static_cast <float> (size)}; //0,0 to size,size
int starCount = min(size/10,random(size/5));
int planetCount = min(size/3,random(size));
std::vector<Star> stars(starCount);
std::vector<Planet> planets(planetCount);
//...
Universe uni(stars, planets);
The rest of the code stays the same. Now, if after the call to create the Universe, you see that the vectors didn't pass the correct information, then look further. The code above conforms to "normal" C++, such that we can go further and figure out the issue.