Bisection method in C++

[Cappo]

Hi,
I wrote befor about the bisection method in C++. This time I managed to make two source's and compile them. But both give me some error that i don't understand. Here are the codes:

#include <iostream> 
#include <stdlib.h> 
#include <math.h> 
 
using namespace std; 
 
double f1( double x) { 
return x*x-pow(1.034554,2); 
} 
double f2( double x) { 
return 2*x; 
} 
 
double bisection(double (*f)(double), 
 
double xL=-100, double xR=100) { 
 
double xN; 
 
if( (*f)(xL)*(*f)(xR) >0) { 
cout << "Error!" << endl; 
return xL; 
} 
 
while (fabs(xL-xR)>0.0001) { 
xN = (xL+xR)/2; 
if( (*f)(xL)*(*f)(xN) <0) 
xR = xN; // i.e. xL and xN have different signs 
// so xRand xN have the same signs 
else 
xL = xN; 
} 
return (xL+xR)/2; 
} 
 
int main() { 
double tmp; 
cout << bisection(f1,-100,100) << endl; 
 system("PAUSE"); 
} 

When i run it here's what comes out on the screen:

Error!
-100
Press any key to continue...

This source(which maybe is not very good):

#include <iostream>
#include <cmath>
#include <stdlib.h> 
#include <math.h> 
using namespace std;
 
int main()
{
int xR, xL,xM, epsilon;
cout <<"Enter a value for the left side: " "\n";
cin >> xL;
cout <<"Enter a value for the right side: " "\n";
cin >> xR;
cout <<"Enter a value for epsilon: " "\n";
cin >> epsilon;
 
  while ((xR - xL) > epsilon)
 
 
  xM = (xR + xL) / 2;
 
 
  if (xL * xM > 0) 
     xL = xM;
  else
 
    xR = xM;
 
system ("pause");
return 0;
}

gives me exactly the same error:

Error!
-100
Press any key to continue...

Could anyone try the program and help me solve the problem.
I need this program working untill 12 o'clock tonight.
Please try to explain the things in a simple way because i am entirely new to programming.
Thank you!

[horace1]

you appear to have your xL and xR start points wrong as there are two roots at -1.03459 and +1.03459 so you test fails
try

cout << bisection(f1,0,100) << endl; 
cout <<  bisection(f1,-100,0) << endl;