problem function Sin()

This is a discussion on problem function Sin() within the C++ Programming forums, part of the General Programming Boards category; i have wrote function Sin(), didn'd use math in libary, but when it run the result error, can you help ...

  1. #1
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    problem function Sin()

    i have wrote function Sin(), didn'd use math in libary, but when it run the result error, can you help me? fix it thanks very much.
    sin(x)=Tn((-1)^k )*(x^2k+1)/(2k+1)!

    Code:
    #include <iostream>
    using namespace std;
    
    double gt(double d){
    	if(d==1||d==0)return 1;
    	return d*gt(d-1);
    }
    //
    double power(double a, int b)
    {
          double c=1;
          for (int h=0; h<b; h++) c*=a;
          return c;
    }
    //
    double Mysin(int x){
    	double Sum=0;
    	for(int i=1;i<=10;i++){
    		double tmp=gt(2*i+1);
    		Sum+=(power(-1,i)*(power(x,2*i+1)))/tmp;
    	}
    	return Sum;
    }
    void main(){
    	//MySin M;
    	int x;
    	cin>>x;
    	cout<<Mysin(x);
    }
    Last edited by llynx; 10-27-2009 at 09:01 AM.

  2. #2
    C++ Witch laserlight's Avatar
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    How does it not work?

    Note that the return type of the global main function is int, not void.
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    Look up a C++ Reference and learn How To Ask Questions The Smart Way

  3. #3
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    it have run, but result error, can you help me ? void ? main<--

  4. #4
    and the Hat of Guessing tabstop's Avatar
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    The first term of sin(x) should be x, not -x. The second term of sin(x) should be -x^3/6, not x^3/6. And so on.

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    thanks 2 you. but i dont use -x, and -x^3/6, not x^3/6.<---i dont understand
    Last edited by llynx; 10-27-2009 at 11:13 AM.

  6. #6
    and the Hat of Guessing tabstop's Avatar
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    Quote Originally Posted by llynx View Post
    thanks 2 you. but i dont use -x, and -x^3/6, not x^3/6.<---i dont understand
    Oh, you're right. You have -x^3/6 correct, you just don't have the x term at all. i needs to start at 0, if you're going to use the 2i+1 form.

  7. #7
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    when i run result still error, if i =0; you help me? thanks
    Code:
    #include <iostream>
    using namespace std;
    
    double gt(double d){
    	if(d==1||d==0)return 1;
    	return d*gt(d-1);
    }
    //
    double power(double a, int b)
    {
          double c=1;
          for (int h=0; h<b; h++) c*=a;
          return c;
    }
    //
    double Mysin(int x){
    	double Sum=0;
    	for(int i=0;i<10;i++){
    		double tmp=gt(2*i+1);
    		Sum+=(power(-1,i)*(power(x,2*i+1)))/tmp;
    	}
    	return Sum;
    }
    void main(){
    	//MySin M;
    	int x;
    	cin>>x;
    	cout<<Mysin(x);
    }

  8. #8
    and the Hat of Guessing tabstop's Avatar
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    Well, the program you have doesn't compile:
    Code:
    H:\temp.cpp:24: error: `main' must return `int'
    changing that gives something that does what I expect. (Notice that I do not expect to get sin(x) out of this program; 10 terms of the series is just not enough if x is even a little bit large (like, say, 10).)

  9. #9
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    your first term is negative because you start your array at one instead of zero (-1 ^ 1 = -1). so you need to add or subtract 1 from i when you use it as an exponent in that first part of the formula.

  10. #10
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    H:\temp.cpp:24: error: `main' must return `int'
    i didn't know u use compler what, but i use visual C++, it still good run, but err result
    i demo 10, realy as 100 .
    your first term is negative because you start your array at one instead of zero (-1 ^ 1 = -1). so you need to add or subtract 1 from i when you use it as an exponent in that first part of the formula.
    but -1^1=-1 yes right, i need it, but result error why ? in where ?

  11. #11
    and the Hat of Guessing tabstop's Avatar
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    Quote Originally Posted by llynx View Post
    i demo 10, realy as 100 .
    I have no idea what this sentence is supposed to mean. If you want your code to accurately compute sin(x), then you will need in certain circumstances to take more than 10 terms of your series. You should then go until the value added on is smaller than your desired tolerance.
    Quote Originally Posted by llynx View Post
    but -1^1=-1 yes right, i need it, but result error why ? in where ?
    This was from your original code where you started in the wrong place.

  12. #12
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    i have add function check(). you can clear it, in -1^1=1. thanks tabstop
    Code:
    #include <iostream>
    using namespace std;
    
    double gt(double d){
    	if(d==1||d==0)return 1;
    	return d*gt(d-1);
    }
    //
    double power(double a, int b)
    {
          double c=1;
          for (int h=0; h<b; h++) c*=a;
          return c;
    }
    int check(int n){
    	return (n%2)==0?1:-1;
    }
    //
    double Mysin(int x){
    	double Sum=0;
    	double tmp=0;
    	for(int i=1;i<10;i++){
    		tmp=gt(2*i+1);
    		Sum+=(check(i+1)*(power(x,2*i+1)))/tmp;
    	}
    	return Sum;
    }
    int main(){
    	//MySin M;
    	int x;
    	cin>>x;
    	cout<<Mysin(x);
    	return 0;
    }

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