I am working with a basic C++ program to determine the area and perimeter of a rectangle. My program works fine for whole numbers but falls apart when I use any number with a decimal. I get the impression that I am leaving something out, but since I'm a complete beginner, I have no idea what.
Below is the source:
#include <iostream>
using namespace std;
int main()
{
// Declared variables
int length; // declares variable for length
int width; // declares variable for width
int area; // declares variable for area
int perimeter; // declares variable for perimeter
// Statements
cout << "Enter the length and the width of the rectangle: "; // states what information to enter
cin >> length >> width; // user input of length and width
cout << endl; // closes the input
area = length * width; // calculates area of rectangle
perimeter = 2 * (length + width); //calculates perimeter of rectangle
cout << "The area of the rectangle = " << area << " square units." <<endl; // displays the calculation of the area
cout << "The perimeter of the rectangle = " << perimeter << " units." << endl; // displays the calculation of the perimeter
system ("pause"); // REMOVE BEFORE RELEASE - testing purposes only
return 0;
}
Change all your int type variables to double or float. I would personally use double because they have more precision than float types.
int datatype stands for integer (i.e. positive and negative whole numbers, including 0)
If you want to represent decimal numbers, you will need to use float.
Use the float or double type, like the others already said.
But it ain't as simple as that. You need to understand what floating-point numbers actually are, and why (0.1 + 0.1 + 0.1) != (0.3). This is a complicated subject, so I won't even try to explain it here - just remember that a float is not a decimal, even if the computer is showing it to you in the form of a decimal.
use floats not ints an integer (int) is a whole number, floats allow decimal places (as do doubles)
float length; // declares variable for length
float width; // declares variable for width
float area; // declares variable for area
float perimeter; // declares variable for perimete
You've defined your variables as integers. Use double instead.
Also, you can look up some formatting for cout to define the number of decimal places you want to show, etc.
Related
I am a complete beginner in programming and I was given the following assignment:
Write a C++ program that computes a pair of estimates of π, using a sequence of inscribed and circumscribed regular polygons. Halt after no more than 30 steps, or when the difference between the perimeters of the circumscribed and inscribed polygons is less than a tolerance of ε=10⁻¹⁵. Your output should have three columns, for the number of sides, the perimeter of an inscribed polygon, and perimeter of the circumscribed polygon. For the last two columns, display 14 digits after the decimal point.
well, I decided to use the law of cos to find the lengths of the sides of the polygon but when I was testing out my program I realized the line:
a = cos(360 / ngon);
keeps giving me a zero as the output which makes everything else also zero and I am not sure what is wrong please help.
P.S. Sorry if the program looks really sloppy, I am really bad at this.
#include "stdafx.h"
#include <iostream>
#include <iomanip>
#include <fstream>
#define _USE_MATH_DEFINES
#include <math.h>
#include <cmath>
using namespace std;
int main()
{
char zzz;
int ngon = 3, a, ak;
double insngon = 0.0;
double cirngon = 0.0;
cout << "Number of Sides" << "\t\t\t" << "Perimeter of insribed region" << "\t\t\t" << "Perimeneter of circumscribed polygon" << "\t\t" << "\n";
while (ngon <= 30)
{
a = cos(360 / ngon);
ak = pow(.5, 2) + pow(.5, 2) - 2 * .5*.5*a;
insngon = (ak*ngon);
cirngon = (ak / (sqrt(1 - pow(ak, 2))));
cout << fixed << setprecision(14) << ngon << " " << insngon << " " << cirngon << endl;
ngon++;
if (cirngon - insngon <= pow(10.0, -15));
cin >> zzz;
return 0;
}
cout << "\nEnter any character and space to end ";
cin >> zzz;
return 0;
}
One issue is that you declared integers, yet you are using them in the call to cos here:
int ngon = 3, a, ak;
//...
a = cos(360 / ngon);
Since a is an integer, the return value of cos (which is of type double) will be truncated. Also, since ngon is an integer, the 360 / ngon will also truncate.
The fix is to make a a double, and divide 360.0 by ngon to prevent the truncation:
int ngon = 3, ak;
double a;
//...
a = cos(360.0 / ngon);
The other issue, as pointed out in the comments is that the trigonometric functions in C++ use radians as the argument, not degrees. You need to change the argument to the equivalent value in radians.
Another issue is that you're using pow to compute values that are constant. There is no need to introduce an unnecessary function call to compute constant values. Just define the constants and use them.
For example:
const double HALF_SQUARED = 0.25
const double EPSILON_VALUE = 10.0e-15;
and then use HALF_SQUARED and EPSILON_VALUE instead of the calls to pow.
Also, pow is itself a floating point function, thus can produce results that are not exact as is discussed by this question . Thus pow(ak, 2) should be replaced with simply ak * ak.
Use float a; (or double a) instead of int a.
Here the return type of a is int
And calculating
a = cos(360/ngon)
Is equivalent to a= cos(120) that is the result of cos(120) is 0.8141 and being a integer type "a" will only store the integer part it.
Therefore 'a' will be 0 and discarding floating value.
Also use double ak; instead of int ak;.
Because here pow function has been used which have return type 'double'
#include <iostream> // try to convert height in centimeters to meters
using namespace std;
int main()
{
int height_cm ; // declaring first int in centimeters
cout << " State your height in centimeters: " << endl ; // stating
cin >> height_cm ; /* I was thinking also of storing this value for later reusage in retyping but I don´t know how to do it */
double (height_cm) ; /* here is the problem,debugger says that I can not declare height_cm again because I had declared it as int before , but I´m actually trying to retype it */
height_cm /= 100 ; /* I´m also not sure about this , I think this assignment should be possible to get number in meters */
cout << " Your height in meters is: " << height_cm << endl ; /* this should give me height in meters */
return 0 ;
}
The problem is that, as your compiler is saying, you are trying to use the same name (height_cm) for another variable. Try doing:
...
double height_m = height_cm/100.0;
cout << " Your height in meters is: " << height_m<< endl ;
...
This way the meter variable will have a new name and the compiler will compile. Moreover, note that I divided height_cm by 100.0 instead of 100. This is because 100 is an int and 100.0 is a float or double. If you use int then you would have an int division meaning that you would lose the decimal part.
A part from that:
I was thinking also of storing this value for later usage in retyping but I don´t know how to do it: The cin>>height_cm; code takes whatever the user has typed, converts it to int and stores it in a variable called height_cm that you can use anytime you want in the current function (in this case main()).
I´m also not sure about this, I think this assignment should be possible to get number in meters: That code would compile with no problem. However, this would end up with an int divison. If you want you can do:
Code:
...
double height_m(height_cm);// this converts the int to double and stores it in the new variable height_m
height_m /= 100;// Divide the double variable height_m by 100 and store it again in height_m
...
Note that in this case although you are using 100 instead of 100.0 that would not be an int division because height_m is a double.
I was instructed to design an algorithm that would allow the user to calculate the perimeter and area of a rectangle, but that's too easy:
Perimeter = 2 (Length + Width)
Area = (Length * Width)
I wanted to build a program using a similar construction to one my professor showed us on the first day so that I could have a program collect data from the user, calculate the perimeter and area of the rectangle for me, and then output the answer back to the user. That was easy enough, so I decided I wanted the program to also tell me whether or not the length and width that the user entered was the length and width of a rectangle or a square.
With the code I wrote, the program always returns that the length and width entered are the length and width of a square. I am not sure where I went wrong:
Here is my code:
#include<iostream>
using namespace std;
int main() {
//Declaration
int length;
int width;
int perimeter;
int area;
//Collect Data
cout << "Let's calculate the perimeter and area of a rectangle\n";
cout << "What is the length of the rectangle?: ";
cin >> (length);
cout << "What is the width of the rectangle?: ";
cin >> (width);
//Calculation
(perimeter) = 2 * (length + width);
(area) = (length) * (width);
//Output Data
cout << "The perimeter of the rectangle is: " << (perimeter) << "\n";
cout << "The area of the rectangle is: " << (area) << "\n";
//For some reason, the code is not able to recognize what I have designed.
//No matter what input for length and width, when the program executes it returns that I entered the length and width of a square.
if ((length) = (width))
cout << "Hey! You entered the length and width of a Square!\n";
else
cout << "You entered the length and width of a Rectangle!\n";
system("pause");
return 0;
}
Any help would be greatly appreciated! Thank you so much!
You want a double equals:
if (length == width)
A single equals (=) performs assignment, double equals (==) performs a comparison.
In your if-statement you are assigning width to length, not comparing.
It should be: if (length == width)
The reason why your if-statement evaluates to true is because it checks whether the result of the evaluation (which is the value of length) is different from zero.
That's because a bool is internally represented as an int, where false is defined as 0 and true else.
And since width is usually not 0 it would always result in true.
You can test it out by entering 0 for width.
One thing I would recommend is looking into using a debugger to step through each line of your code as it runs one at a time. If you are using VS you have one built right in!
I think if you used a debugger you would have noticed that when the if was running it was doing the assignment rather than the comparison. Just a thought for the future.
I'm sure everyone can say they have caught many silly bugs with a debugger. Good job :)
Hey this is really one of the first things I've ever coded. I was wondering how might I fix this error. I am currently trying to do some research but can't find anything that is helpful in fixing it.
#include <iostream> // needed for Cin and Cout
#include <cmath>
#include <csmath>
using namespace std;
/************************************
* defines
*************************************/
#define PI 3.14159
/*************************************
* function prototype
*************************************/
int main()
{
//surface and volume
float radius;
float height;
float surfacearea;
float volume;
int pi = 3.14159
//Get the radius
cout << "enter the radius: ";
cin >> (float)radius;
//Get height
cout << "enter height: ";
cin >> height;
//Get the surfacearea
surfacearea = 2(pi*radius^2)+2(pi*radius)* height;
cout << "The surfacearea is: " << surfacearea;
//get volume
volume = (pi*radius)^2*height;
cout << "The volume is: " << volume << endl;
system ("pause");
return 0;
}
Change int to double for pi, because pi is a floating point number, which, as stated in the comments, is C++'s default for floating point numbers. Unless there is a particular reason to use float, use double for floating-point numbers.
double pi = 3.14159;
And the warning will go away.
Also, you don't have to cast your input to float, simply:
cin >> radius;
Additionally, at the very least, change radius^2 to radius*radius.
But better yet, avoid ^ altogether and use std::pow, an example of which can be found here.
Additionally, you don't need to #define PI 3.14159 because you never use it, and you try to define pi in main().
You better declare and initialize local variables right before you need them. For constants like pi you better use const and proper type. For a proper type C++11 offers you a great tool - auto. And ^ does not mean power in C++ you have to use std::pow() instead. So your code should look like this:
const auto pi = 3.14159;
//Get the radius
auto radius = 0.0;
cout << "enter the radius: ";
cin >> radius;
//Get height
auto height = 0.0;
cout << "enter height: ";
cin >> height;
//Get the surfacearea
auto surfacearea = 2 * pi * pow( radius, 2.0 ) + 2 * pi * radius * height;
cout << "The surfacearea is: " << surfacearea << endl;
//get volume
auto volume = pow( pi*radius, 2.0 ) * height;
cout << "The volume is: " << volume << endl;
To begin with, a warning is not an error; if it were a compilation error, then the code would not even compile. However, since it was a warning, that means your code did compile successfully and run, except that it produced a warning about something in your code. Now to the bugs in your code:
Firstly, your declaration for the local variable pi is incorrect. pi is declared in your code as a variable of data type int, short for integer. An integer is only a whole number, positive and negative one, but one that is neve more specific than 10^0. Now the problem is that you are trying to store a decimal value in an int variable. While the compiler is able to make a conversion of the decimal value into an int value, you lose the precision of the value; that's because it rounds the value. If you compile this sample code:
int floating = 1.23456789;
cout << floating << endl;
It will output 1 instead of 1.23456789, with the reason being that an int variable cannot store a float or double value; it however can convert this float or double value into an int value by rounding it.
Therfore, you should change your declaration for pi to:
double pi = 3.14159; // By the way, you forgot to add a semicolon here
Another problem: you are using unnecessary typecating in your cin statement for the radius:
cin >> (float)radius;
You would need to use casting if you want to change the data type of a variable for a particular operation (you don't change the variable data type; you merely process its value as the data type cast. In your case, it is unrequired, because the radius variable is already declared as a data type of float, in the line:
float radius;
Therefore, I would recommend you to simply change this cin statement to:
cin >> radius;
One more thing: the following lines in your code have a problem:
surfacearea = 2(pi*radius^2)+2(pi*radius)* height;
volume = (pi*radius)^2*height;
The "^" symbol does not raise a number to a power; it is called a bitwise XOR operator in c++ and it server the purpose of copying the bit if it is set in one operand but not both. You can find more information about it here: Bitwise Exclusive OR Operator: ^
In c++, if you want to raise a number x to a power like 2, then you have to do x * x. Alternatively, you can use the pow() function like: pow(x, 2.0). For your code, if we use the x*x method, it would be like:
surfacearea = 2(pi*radius*radius)+2(pi*radius)* height;
volume = (pi*radius)*(pi*radius)*height;
Alternatively, if we use the pow() function, then the code would look like:
surfacearea = 2(pi*pow(radius, 2))+2(pi*radius)* height;
volume = pow((pi*radius), 2)*height;
Fixing these peoblems should get your code to work.
What would be the best variable type for storing GPS coordinates in a C++ program? I wrote the code below just to try it out and regardless of what variable types I chose the problem persisted.
#include<iostream>
#include<algorithm>
#include<math.h>
using namespace std;
class Coordinate {
public:
float xcoor, ycoor;
int radius;
void set_values (float, float, int);
};
void Coordinate::set_values (float x, float y, int r){
xcoor = x;
ycoor = y;
radius = r;
}
int main (){
Coordinate test;
test.set_values (32.682633, -117.181554, 50);
cout << "coordinates: (" << test.xcoor << "," << test.ycoor << ")\n";
return 0;
}
This code outputs the values:
(32.6826,-117.182)
So obviously I am losing huge amounts of precision, but is there anyway I could maintain it? I haven't done GPS coordinates before and couldn't find anyone with a similar problem.
Thank you for your help.
using floating point variables in arithmetic can lead in a loss of precision, but as far as I see you do not do any calculation with your coordinates.
I suspect that you are assuming that std::cout does output floating point variables with full precision, which is not the case by default.
double test = 1.23456789;
std::cout.precision(10);
std::cout << "test: " << test << std::endl; // prints "test: 1.23456789"
See that question, as well as the documentation of ostreams for further information.
As far as I can see it only prints 6 digits. Try either setw or setprecision. With the former you can set a constant with to print out numbers or characters (this comes handy at aligning), the latter sets how many digits your program prints.
With floats you shouldn't lose any data from those numbers.