for those that are good with c++ (1 Viewer)

[A2RAYA]

hey all...if anyone here knows their c++ programs..i need some help with a couple of programs i'm writing for uni

1)

//prac week 13-Q1
//program will ask the user to enter a value (x) and then use it in one of two functions,
//depending on its size,to return a value for the function g(x)

#include <iostream.h>
#include <stdlib.h>
#include <math.h>

double g(double x1),
double g_2(double x2);

void main()
{
	double x;

	cout<<"enter a number: ";
	cin>>x;

	if(x<0)
	{
		 g(x);
	}

	if(x>=0)
	{
		  g_2(x);
	}

	//--------------------------------------------------------------------------------


	  double g(double x)

-->{
		cout<<"g(x)= 0"<<endl<<endl;
}

	//--------------------------------------------------------------------------------

 double g_2(double x)

-->{	
		cout<<"g(x)= "<<(6*exp(x-3))<<endl;
}

	return;
}

now i can't see a prob with this but then i compile it and it says:
error C2601: 'g' : local function definitions are illegal
error C2601: 'g_2' : local function definitions are illegal

any ideas?
cheers

 

[Slidey]

#include <iostream.h>
#include <stdlib.h>
#include <math.h>

double g(double x1);
double g_2(double x2);

int main()
{
    
double x;
cout<<"enter a number: ";
cin>>x;
if(x<0)
{
g(x);
}
else if(x>=0)
{
g_2(x);
}
system("pause");
return 0;
}

double g(double x)
{
cout<<"g(x)= 0"<<endl;
}

double g_2(double x)
{ 
cout<<"g(x)= "<<(6*exp(x-3))<<endl;
}

 

[A2RAYA]

thanks heaps slide....but now the b**tards have given us an even harder one...heres it is if u wana try it :

"The factorial of a nonnegative integer n is written n! and is defined as follows:
n! = n*(n-1)*(n-2)* ….*1 (for values of n =>1)
and
n! = 1 (for n = 0).

The cosine of an angle can be computed from the following infinite series:

cos x= 1- x^2/2! + x^4/4! + x^6/6 + .......


Write a program that reads an angle x (in radians) from the keyboard and the number of terms to be used in the series. Then, in a function, compute the cosine of the angle using the terms specified for this series. Print the value computed along with the value of the cosine computed using the C++ library function."

 

[Slidey]

Here's something on factorials to get you started, but since this is presumably a uni assignment, I am not going to code the programme for you:

#include<iostream.h>
int main()
{
    int n=0;
    cin >> n;
    int a=n;
    if(n==0)//case where 0!=1
    {
        cout << n << "! is 1\n";
    }
    else if(n>0)//where n is a natural number
    {
        int result=1;
        for(int i=0;i<n;i++)
        {
            result=result*(a-i); 
        }   
        cout << n << "! is " << result << endl; 
    }
    else//case where n is negative
    {
        cout << "Invalid input.\n";
    }           
    system("pause");
    return 0;
}

Think about how I used the for loop as you'll want to that to generate your cosine approximation.

Feel free to ask for any clarification.

 

[sunny]

Factorials are recursive by definition - the easiest way to solve it is to write a 3 or 4 line recursive program - much simpler than using iterations.

 

[Slidey]

Didn't I use recursion? Actually, I can't tell the difference.

 

[HellVeN]

That's cause you're a noob at life Slimer.


Recursion <> Repetition

 

[jm1234567890]

Factorials are recursive by definition - the easiest way to solve it is to write a 3 or 4 line recursive program - much simpler than using iterations.

we were always taught that recursion uses more resources and is less efficient than repetition and should be avoided.

then again, we will be so screwed at programming competitions.

 

[Slidey]

Feel free to explain the difference to me.

 

[acmilan]

Recursion = when a method calls itself, or at least thats what its used for in java, havent tried doing it on c++ yet

 

[jm1234567890]

http://en.wikipedia.org/wiki/Recursion

http://en.wikipedia.org/wiki/Iteration

 

[sunny]

we were always taught that recursion uses more resources and is less efficient than repetition and should be avoided.

then again, we will be so screwed at programming competitions.

This is generally true, but for most problems this is irrelevant. When it is relevant, you can still use dynamic programming over iterative methods. For most problems n has to be fairly big or computationally expensive to have much difference.

Recursion = when a method calls itself, or at least thats what its used for in java, havent tried doing it on c++ yet

Recursion is a general programming technique - it will work in any high level language.

 

[jm1234567890]

This is generally true, but for most problems this is irrelevant. When it is relevant, you can still use dynamic programming over iterative methods. For most problems n has to be fairly big or computationally expensive to have much difference.

Why can't you use dynamic prgramming methods with recursion?

 

[sunny]

You can !

 

[jm1234567890]

You can !

lol, i completely misread your post