Execution time comparison [duplicate] - c++

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How to Calculate Execution Time of a Code Snippet in C++
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I have a snowball launcher game codes. There is a arm to launch snowball and the target in the game. I have 2 different block of codes that makes the calculation for releasing angle of the arm with the input of length of the arm and target's x and y coordinates. One of them is:
#include <iostream>
#include <cmath> // math library
#include <windows.h> // system()
using namespace std;
class SnowballMachine{
private:
double L,X,Y, theta; //L for Lenght of the arm, X and Y is the coordinates
const double pi = 3.14159265; //Theta=Release angle
public:
void input() //get inputs for lenght of the arm and coordinates
{
cout<<"Please enter the coordinations of the target(for Target(x,y) enter 40 28)" <<endl;
cin>>X>>Y;
cout<<"Please enter the length of the arm: "<<endl;
cin>>L;
}
double calculate(){ //calculates the release angle with perpendicular slope comparison
if(L*Y <= X*sqrt(pow(Y, 2.0)+pow(X, 2.0)-pow(L, 2.0)))
{
theta=asin((L*Y + X*sqrt(pow(Y, 2.0)+pow(X, 2.0)-pow(L, 2.0)))/(pow(Y, 2.0)+pow(X, 2.0)));
return theta;
}
else
{
theta=asin((L*Y - X*sqrt(pow(Y, 2.0)+pow(X, 2.0)-pow(L, 2.0)))/(pow(Y,2.0)+pow(X, 2.0)));
return theta;
}
}
void ThetaDisplay() //displays output
{
cout << "The releasing angle is "<<180-(theta*180/pi)<<" degrees"<<endl;
}
};
//const values for options to get input
const int OPEN_GATE=1 ;
const int LOAD_SNOWBALL = 2;
const int ADJUST_ARM=3;
const int RELEASE_ARM=4;
const int QUIT=5;
int menu(); // get a command
void execute(int, SnowballMachine &Dummy); // run a given command
int main()
{
SnowballMachine A; //calling the class
A.input(); //calling the functions
A.calculate();
int choice;
A.ThetaDisplay();
do //select the options
{
choice = menu();
execute(choice, A);
} while (choice != QUIT );*/
return 0;
}
int select;
system("cls");
do
{
cout <<"1....Open the gate\n";
cout <<"2....Load the Snowball\n";
cout <<"3...Adjust the arm\n";
cout <<"4....Release the Snowball\n";
cout<<"5...Quit\n";
cout <<"enter selection: ";
cin >> select;
} while (select!=1 && select!=2 && select!=3 && select!=4 &&select!=5);
return select;
}
void execute(int cmd, SnowballMachine &Dummy)
{
//options switch method
switch (cmd)
{
case OPEN_GATE: cout << "Opening the gate\n";
break;
case LOAD_SNOWBALL: cout << "Loading the snowball\n";
break;
case ADJUST_ARM:cout<<"Adjusting the arm\n";
break;
case RELEASE_ARM:cout<<"Releasing the arm\n";
Dummy.calculate();
Dummy.ThetaDisplay();
break;
case QUIT:cout<<"Quitting!!!";
break;
default:
cout <<" Invalid Entry. Try it again please.";
}
This is the first one. Second one is:
This is the main.cpp
#include <iostream>
#include "Snowball.h"
using namespace std;
int main()
{
Snowball A;
A.Display();
A.ArmLength();
A.Input();
A.SetStartPOS();
for(double i = A.getLength(); i>A.getStartPOS(); i-=A.DELTAX)
{
if (A.Derivative(A, i)*.9999 >= ((A.getY()-A.foo(i))/(A.getX()-i))*1.0001)
{
A.setxPointcirc(i);
break;
}
}
A.AngleDisplay();
return 0;
}
This is the part of main.cpp which is snowball.cpp which calls all the functions:
#include "Snowball.h"
#include <iostream>
#include <cmath>
#include <iomanip>
using namespace std;
void Snowball::Input()
{
cout << "Enter the x-postion of the target: ";
cin >> x;
while(x < armlength || x < armlength*-1)
{
cout << endl;
cout << "Please make sure your x is greater than " << armlength << '.' << endl;
cout << "Enter the x-postion of the target. ";
cin >> x;
}
cout << "Enter the y-postion of the target: ";
cin >> y;
while(y < 0 || (y < armlength && x<armlength) )
{
cout << endl;
cout << "Enter the y-postion of the target: ";
cin >> y;
}
this->x =x;
this->y =y;
}
void Snowball::ArmLength()
{
cout << "Enter the Length of the Arm: ";
cin >> armlength;
this->armlength =armlength;
}
void Snowball::Display()
{
cout << "Welcome to the Snowball Launcher. \n\n";
}
double Snowball::foo(double x)
{
double z;
z = sqrt(powf(armlength, 2.0)-powf(x, 2.0));
return z;
}
double Snowball::Derivative(Snowball &foo_dummy, double x)
{
return (foo_dummy.foo(x+DELTAX/2.0) - foo_dummy.foo(x-DELTAX/2))/DELTAX;
}
void Snowball::AngleDisplay()
{
theta = rad2deg(acos(xPointCircle/armlength));
cout << "\nTarget Destroyed.\nAngle Required is: " << theta << " degrees." << setprecision(4) <<endl;
}
void Snowball::SetStartPOS()
{
StartPOS = armlength*-1;
}
void Snowball::setxPointcirc(double i)
{
xPointCircle = i;
}
And here is the getters and setters with declaring the const and variables header:
#ifndef SNOWBALL_H_INCLUDED
#define SNOWBALL_H_INCLUDED
#include <iostream>
#include <cmath>
using namespace std;
class Snowball {
private:
double rad2deg(double h) {return h*(180/pi); };
double x, y, theta, xPointCircle, StartPOS, armlength;
public:
static const double pi = 3.1415926535897;
static const double DELTAX = 0.001;
double foo(double x);
double Derivative(Snowball &foo_dummy, double x);
void Display();
void Input();
double getLength() {return armlength; }
double getStartPOS() {return StartPOS; }
double getY() {return y; }
double getX() {return x; }
void setxPointcirc(double i);
void ArmLength();
void AngleDisplay();
void SetStartPOS();
};
#endif
Here is my question: I get the same results with both 2 different block of codes. I want to
test which execution time is less(which one would be faster?).

Answer 1

Generally the way this is approached is to call the function n number of times (for large n) and calculate the time taken across the calls.
For instance, call it "the first way" 100000 times (getting the time before and time after) then calculate it "the second way" the same number of times (again checking the time before and after). By subtracting the two, you'll get a decent estimate of which is faster/slower.
Note that you need to test it many numbers of times to get an accurate result, not just once!