Equation with functions (C++)

[iAmChapin]

It's me again hehe.. well, i have to do 10 exercises in C++. I already did 9. I'm here because i can't understand the last one... i have the sigma function of the equation only, but i don't know how to do the other part (xi/i!). This is the excersice:

http://oi58.tinypic.com/x4kxtk.jpg

It is repeated twice , just down I translated it into English so that it is understood since I speak Spanish. So you know now that what i'm saying with the "xi/i!" part. Here is my code with the sigma (i=1 Σ n) part:

  #include <iostream>
#include <conio.h>
#include <windows.h>
using namespace std;

//FUNCTION SIGMA
int sigma(int a, int b){

int sum = 0;


//THIS SUM I TO N
	for (int i=0; i<=a; i++){
   	sum = sum+i;
      }

   return sum;

}

int x;    //GLOBAL VARIABLES INT
int n;

int main(){

textcolor(11);
gotoxy(6,4); cprintf("I can solve sigma");
textcolor(15);
gotoxy(24,6); cprintf("Enter N: ");
cin >> x;
textcolor(15);
gotoxy(24,8); cprintf("Enter X: ");
cin >> n;
//PRINT THE RESULT
textcolor(15);
gotoxy(24,10); cprintf("Result is: "); cout << sigma (n, x);

getch();
return 0;
}

That's all, but i don't know what to do with X and the other part of the equation :( if anyone please can give me a solution for this!? Thank you for reading!!

[helios]

Is the problem poorly stated? It says to "solve" the equation, but it doesn't say which variables are known and which are unknown. Are they all unknown? Is (R = 0, n = 1, x = 0) a solution?

[iAmChapin]

The engineer who teaches us told us that R has to be found with Equation.
He gave us a little guide he made in a program but i did not understand it , I'll show you:

http://oi58.tinypic.com/x5ayw6.jpg

[helios]

OK, so it's not really "solve" then, but "implement".

Your summation is not implemented correctly. You need to compute x / 1 + x^2 / 2 + x^3 / 6 + x^4 / 24 + ... + x^n / n!. You're only computing 0 + 1 + 2 + 3 + ... + n

[iAmChapin]

I know, but thats why i'm asking for the solution, i don't know too much of C++ thats why i'm studying, so, if you can write the code for me, i will thank you helios!

[helios]

Well, time to start learning, eh?

x^0 = 1
x^1 = 1 * x
x^2 = 1 * x * x
x^3 = 1 * x * x * x
etc.

0! = 1
1! = 1
2! = 1 * 2
3! = 1 * 2 * 3
etc.

Figure out how to do this with loops. Notice that you sigma function is already very similar to a factorial implementation.

[iAmChapin]

Thanks helios, i did it but the result isn't the same at the final. I'll show you the code and if you detect the problem, please, tell me, thank you!

#include <iostream>
#include <conio.h>
#include <windows.h>
#include <math.h>
using namespace std;

//FUNCTION SIGMA
float sigma(float a, float b){

float division;
float sum = 0;
float operation = 1;
float i = 1;

	while(i <= b){
         a = pow (a,i);
   		for (int z = 1; i <= b; z++){
         operation = operation*z;
         division = a / operation;
      	sum = division+sum;
         i++;
       }
    }
    return sum;
}

int x;    //GLOBAL VARIABLES INT
int n;

int main(){

gotoxy(6,4); cprintf("I can solve sigma");
textcolor(15);
gotoxy(24,6); cprintf("Enter X: ");
cin >> x;
textcolor(15);
gotoxy(24,8); cprintf("Enter N: ");
cin >> n;
textcolor(15);
gotoxy(24,10); cprintf("Result is: "); cout << sigma(x, n);

getch();
return 0;
}

[helios]

Line 16: Work out in paper what values a will take each time through the loop. Don't write it numerically, the math expression will do.

Also:
1. Fix your indentation. Your code is impossible to follow.
2. Once you do that, you should see another reason why the code doesn't work.

[Ericool]

If I can give you an hint , look for recursive function in Google.

The method should not take more than 10 lines of code for sure.

This is not an iterative method. It is a fast method call technique but that will increase the call stack frame size so make sure to start with 10 or something not 4000 !

Reply with a recursive function and then we can help you with arithmetics.

Good search !