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Uninitialized variable behaviour in C++
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Here are the errors on the following code after the VS2022(v143) upgrade:
Could someone please suggest what is wrong here and how to fix it?
//Cricle properties problem
#include <iostream>
using namespace std;
float Qradius(float diameter)
{
float radius = diameter / 2;
return radius;
}
float Warea(float radius)
{
float area = (radius *radius) *3.14;
return area;
}
float Ecircumference(float diameter)
{
float circumference = 3.14 * diameter;
return circumference;
}
float Rarclength(float arcangle, float circumference)
{
float arclength = (circumference *arcangle) / 360;
return arclength;
}
int main()
{
float diameter, arcangle;
float area, circumference, arclength, radius;
cout << "Type the diameter ";
cin >> diameter;
cout << "Type the arcangle ";
cin >> arcangle;
cout << "The radius of the circle is " << Qradius(diameter) << endl;
cout << "The area is " << Warea(radius) << endl;
cout << "The circumference is " << Ecircumference(diameter) << endl;
cout << "The arc length is " << Rarclength(arcangle, circumference) << endl;
}
I solved the warnings and explained why they were coming up in the comments in the code. Also do not use using namespace std;
#include <iostream>
float Qradius(float diameter)
{
float radius = diameter / 2;
return radius;
}
float Warea(float radius)
{
// if no f is specified, the compiler assumes it is a double
// the warning tells you that it converts a double to float
// which could lead to loss of data (C4244)
float area = (radius *radius) * 3.14f;
return area;
}
float Ecircumference(float diameter)
{
// same as aboth
float circumference = 3.14f * diameter;
return circumference;
}
float Rarclength(float arcangle, float circumference)
{
float arclength = (circumference *arcangle) / 360;
return arclength;
}
int main()
{
float diameter, arcangle;
// area and arclength are unused (C4101)
float /*area,*/ circumference, /*arclength,*/ radius;
std::cout << "Type the diameter ";
std::cin >> diameter;
std::cout << "Type the arcangle ";
std::cin >> arcangle;
// radius and circumference is never set
// and later used without setting any value (C6001)
radius = Qradius(diameter);
circumference = Ecircumference(diameter);
std::cout << "The radius of the circle is " << radius << std::endl;
std::cout << "The area is " << Warea(radius) << std::endl;
std::cout << "The circumference is " << circumference << std::endl;
std::cout << "The arc length is " << Rarclength(arcangle, circumference) << std::endl;
}
I got an error in Visual Studio 2019, when building and using IntelliSense at the same time, which said that it expected a ';' (CODE: E0065 and the error is supposed to be on line 9), I am extremely confused because this is my first time getting an error like this when defining functions because it is also my first time defining functions in c++, I really don't know where I could be missing a semi colon. The program doesn't run.
#include <iostream>
using namespace std;
int main() {
const double pi{3.14159};
double calc_area_circle(double radius) {
return pi * (radius * radius);
}
void area_circle() {
double radius{};
cout << "Enter the radius of the circle: ";
cin >> radius;
cout << "The area of the circle with radius " << radius << " is " << calc_area_circle(radius) << endl;
}
return 0;
}
If any one could clear this up for me, I would really appreciate it.
Nesting of function definition (defining functions inside another functions) is not allowed in C++ unless you use lambda functions.
Put the function definitions outside the function
#include <iostream>
using namespace std;
const double pi{3.14159};
double calc_area_circle(double radius) {
return pi * (radius * radius);
}
void area_circle() {
double radius{};
cout << "Enter the radius of the circle: ";
cin >> radius;
cout << "The area of the circle with radius " << radius << " is " << calc_area_circle(radius) << endl;
}
int main() {
return 0;
}
or convert them to lambda function
#include <iostream>
using namespace std;
int main() {
const double pi{3.14159};
const auto calc_area_circle = [&](double radius) -> double {
return pi * (radius * radius);
};
const auto area_circle = [&]() {
double radius{};
cout << "Enter the radius of the circle: ";
cin >> radius;
cout << "The area of the circle with radius " << radius << " is " << calc_area_circle(radius) << endl;
};
return 0;
}
Note: these programs will do nothing because the defined functions are not called.
#include <iostream>
#include <iomanip>
using namespace std;
int main()
{
const double PI = 3.14159;
double rad = 0;
double area = 0;
double vol = 0;
int areaPi = 0;
int volPi = 0;
cout << setprecision(5) << fixed;
cout << setw(38) << left << "Enter radius for the sphere: " << right);
cin >> rad;
area = (4 * PI * (rad * rad));
vol = ((4.0/3.0) * PI * (rad * rad * rad));
areaPi = (4 * (rad *rad));
volPi = (4 * (rad * rad * rad));
cout << right << "Surface area of the sphere: " << setw(12) << area << " (" << areaPi << "\u03C0)";
cout << "\n";
cout << "The volume of the sphere: " << setw(14) << vol << " (" << volPi << "π/3)";
cout << "\n";
return 0;
}
Hi guys. So the problem I'm having is that when you enter a value for the radius (rad) variable the cursor wants to work its way from the left to the right when the user types resulting in double digit numbers being longer than the output columns.
It looks like this when the program runs and you enter anything longer than one digit:
//Enter radius for the sphere: 17
//Surface area of the sphere: 3631.67804 (1156π)
//The volume of the sphere: 20579.50889 (19652π/3)
I would like the 7 to line up with the column below it. I tried setting the width to one less than I had before & single digits end up one space too far to the left like so:
//Enter radius for the sphere: 4
//Surface area of the sphere: 201.06176 (64π)
//The volume of the sphere: 268.08235 (256π/3)
I would store the output into a set of strings. Then you could check and manipulate the data as needed. Alternatively you could calculate the offset of spaces you'd need before printing
// convert to string for digit count
std::string output_1 = std::to_string(x);
std::string output_2 = std::to_string(y);
int o_1_2_dist = output_1.size() - output_2.size(); // difference in digits
std::string padding_1, padding_2;
if (o_1_2_dist < 0)
padding_1 = std::string(abs(o_1_2_dist), ' ');
else
padding_2 = std::string(o_1_2_dist, ' ');
std::cout << padding_1 << output_1 << '\n' << padding_2 << output_2;
you'd want to adjust on of the output strings so it doesn't count the extra bits of the number you don't care about. Maybe do output_1 = std::to_string(floor(x)); or something like that so you don't count the digits after the decimal
This can be solved by calculating the length of the input. I used c++11's to_string to convert the resulting values to strings and find out their lengths. I haven't tried how portable that is. It seems to work under linux with gcc 6.1.1., but for some reason it did not work with the input, so I changed that part as well so that the users enters a std::string which gets converted to a double afterwards.
#include <iostream>
#include <iomanip>
using namespace std;
int main()
{
const double PI = 3.14159;
double rad = 0;
double area = 0;
double vol = 0;
int areaPi = 0;
int volPi = 0;
int width_col1 = 40;
//cout.fill('.');
cout << setprecision(5) << fixed;
cout << left << setw(width_col1) << "Enter radius for the sphere: " << right;
std::string input;
cin >> input;
rad = stod(input);
area = (4 * PI * (rad * rad));
vol = ((4.0/3.0) * PI * (rad * rad * rad));
areaPi = (4 * (rad *rad));
volPi = (4 * (rad * rad * rad));
int indent = width_col1 + input.length() + 1;
cout << left << setw(indent - to_string(area).length()) << "Surface area of the sphere: " << area << " (" << areaPi << "\u03C0)" << std::endl;
cout << left << setw(indent - to_string(vol).length()) << "The volume of the sphere: " << vol << " (" << volPi << "π/3)" << std::endl;
return 0;
}
This solution resembles what C programmers would have done with printf.
I would love to learn why this did not work with the input.
The calculation for dx and dy is returning 0 and I don't see what the issue is. The console seems to show all the correct values are being used.
void drawBackground()
{
double r, g, b, dx, dy, Wx, Wy, Wz;
Ray ray;
cout << "xmax: " << sceneDescription::imagePlaneXmax << " xmin: " << sceneDescription::imagePlaneXmin << endl;
cout << "ymax: " << sceneDescription::imagePlaneYmax << " ymin: " << sceneDescription::imagePlaneYmin << endl;
cout << "Iw: " << sceneDescription::Iw << " Ih: " << sceneDescription::Ih << endl;
cout << " " << endl;
dx = (sceneDescription::imagePlaneXmax - (sceneDescription::imagePlaneXmin))/sceneDescription::Iw;
dy = (sceneDescription::imagePlaneYmax - (sceneDescription::imagePlaneYmin))/sceneDescription::Ih;
std::cout << "dx: "<< boost::format("%1$.16f") % dx << " dy: "<< boost::format("%1$.16f") % dy << endl;
}
sceneDescription.h
#include <glm/glm.hpp>
using namespace glm;
class sceneDescription{
public:
static const int imagePlaneXmin = -1;
static const int imagePlaneXmax = 1;
static const int imagePlaneYmin = -1;
static const int imagePlaneYmax = 1;
static const int Iw = 600;
static const int Ih = 800;
};
Console output:
xmax: 1 xmin: -1
ymax: 1 ymin: -1
Iw: 600 Ih: 800
dx: 0.0000000000000000 dy: 0.0000000000000000
The problem is that the statement:
dx = (sceneDescription::imagePlaneXmax -
(sceneDescription::imagePlaneXmin))/sceneDescription::Iw;
will give the following result:
(1-(-1))/600 = 2/600 = 0.00 (since this is integer division).
You may want to cast the number to double.
Something like this would work:
dx = (double)(sceneDescription::imagePlaneXmax -
(sceneDescription::imagePlaneXmin)) / sceneDescription::Iw;
Since cast operator has higher priority than division, the numerator will be cast by (double) and the denominator will be cast implicitly giving the double result.
Hope that helps!
I am trying to solve a quadratic equation using the bisection method. When trying to evaluate the roots I get this error: "no matching function for call".
#include "assign4.h"
#include <iostream>
using namespace std;
int main(int argc, char * argv[]){
solution s;
double root;
cout << "Enter interval endpoints: ";
cin >> s.xLeft >> s.xRight;
cout << "Enter tolerance: ";
cin >> s.epsilon;
root = s.bisect (s.xLeft, s.xRight, s.epsilon, s.f, s.error);
if (!(s.error))
cout << "Root found at " << root << "\nValue of f(x) at root is: " << s.f(root);
else
cout << "The solution of a quadratic equation with coefficients: " << endl;
cout << "a = " << a << ", b = " << b << ", c = " << c << endl;
cout << "has not been found." << endl;
return 0;
}
The error occurs where root = ... it seems to have a problem with my function f but I don't understand what is wrong. The following two bits of code are my class and class implementation files. We just started working with classes so I am uncertain if my problem lies there or simply in the above code.
#ifndef ASSIGN4_H
#define ASSIGN4_H
class solution {
public:
double xLeft, xRight;
double epsilon;
bool error;
double bisect(double, double, double, double f(double), bool&);
double f(double);
};
#endif // ASSIGN4_H
//////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
#include "assign4.h"
#include <iostream>
#include <cmath>
using namespace std;
double solution::bisect (double xLeft, double xRight, double epsilon, double func(double), bool& error) {
double xMid;
double fLeft, fRight;
double fMid;
fLeft = f(xLeft);
fRight = f(xRight);
error = (fLeft * fRight) > 0;
if (error)
return -999.0;
while (fabs (xLeft - xRight) > epsilon) {
xMid = (xLeft + xRight) / 2.0;
fMid = f (xMid);
if (fMid == 0.0)
return xMid;
else if (fLeft * fMid < 0.0)
xRight = xMid;
else
xLeft = xMid;
cout << "New Interval is [" << xLeft << ", " << xRight << "]" << endl;
}
return (xLeft + xRight) / 2.0;
}
double solution::f (double x) {
return ((5 * pow(x,2.0)) + (5 * x) + 3);
}
The 4th parameter is a function pointer,
double bisect(double, double, double, double f(double), bool&);
When you call this function:
root = s.bisect (s.xLeft, s.xRight, s.epsilon, s.f, s.error);
While the member fiction double f(double) is not the same type as that parameter because this is C++ member function and not static, so the 'this' parameter is added this member function when compiling.
type add the static key word to the function.
The syntax for a function pointer is usually: double (*f)(double). Aside from that, you are attempting to pass a member function through a non-member-function pointer. Since your function does not use any member variables, the simplest solution would be to make it static:
class solution {
// ...
static double f(double);
};
If you want to use pointers to member functions.
Change
double bisect(double, double, double, double f(double), bool&);
to
double bisect(double, double, double, double (solution::*f)(double), bool&);
in declaration and definition.
Change the call from
root = s.bisect (s.xLeft, s.xRight, s.epsilon, s.f, s.error);
to
root = s.bisect (s.xLeft, s.xRight, s.epsilon, &solution::f, s.error);
This is what I have that compiles and links successfully for me.
#include <iostream>
#include <typeinfo>
#include <math.h>
using namespace std;
class solution {
public:
double xLeft, xRight;
double epsilon;
bool error;
double bisect(double, double, double, double (solution::*f)(double), bool&);
double f(double);
};
using namespace std;
double solution::bisect (double xLeft, double xRight, double epsilon, double (solution::*func)(double), bool& error) {
double xMid;
double fLeft, fRight;
double fMid;
fLeft = (this->*func)(xLeft);
fRight = (this->*func)(xRight);
error = (fLeft * fRight) > 0;
if (error)
return -999.0;
while (fabs (xLeft - xRight) > epsilon) {
xMid = (xLeft + xRight) / 2.0;
fMid = (this->*func)(xMid);
if (fMid == 0.0)
return xMid;
else if (fLeft * fMid < 0.0)
{
xRight = xMid;
fRight = fMid;
}
else
{
xLeft = xMid;
fLeft = fMid;
}
cout << "New Interval is [" << xLeft << ", " << xRight << "]" << endl;
}
return (xLeft + xRight) / 2.0;
}
double solution::f (double x) {
return ((5 * pow(x,2.0)) + (5 * x) + 3);
}
int main(int argc, char * argv[]){
solution s;
double root;
cout << "Enter interval endpoints: ";
cin >> s.xLeft >> s.xRight;
cout << "Enter tolerance: ";
cin >> s.epsilon;
root = s.bisect (s.xLeft, s.xRight, s.epsilon, &solution::f, s.error);
if (!(s.error))
cout << "Root found at " << root << "\nValue of f(x) at root is: " << s.f(root) << endl;
else
{
cout << "The solution of a quadratic equation with coefficients: " << endl;
// cout << "a = " << a << ", b = " << b << ", c = " << c << endl;
cout << "has not been found." << endl;
}
return 0;
}
I believe it has to do with your callback function. Typically you get that kind of compiler error when you use an incorrect function call. If you want this kind of callback function, you may want to look into function pointers.
http://www.cprogramming.com/tutorial/function-pointers.html