Thread: problem with the bisection method

HI!
I wrote a program that finds a root with the bisection method.
The problem is that i cant find the bug :P
here is the code...
can you give me your ideas for solving the problem?

Code:

#include<stdio.h>
double my_function(double x);
double a,b,e,meso,fm,fa,fb;
int main()
{
    printf("GIVE {a} AND {b} OF THE INTERVAL [a,b] \n,AND   ALSO THE TOLERANCE e:");
    printf("EXAMBLE:IF a=1 AND b=2 GIVE 1 2\n");
    scanf("%lf%lf%lf ",&a,&b,&e);
	 fa=my_function(a);
	 fb=my_function(b);
    while((fa>0)&&(fb>0) || (fa<0)&&(fb<0))
        {
    printf("THE VALUES A AND B DO NOT DIFFER IN SIGN\n");
            printf(" (+a)*(+b) OR (-a)*(-b) WORNG\n");
            printf("GIVE {a} AND {b} OF THE INTERVAL [a,b] \n,AND ALSO THE TOLERANCE e:");
            scanf("%lf%lf%lf",&a,&b,&e);
	 fa=my_function(a);
	 fb=my_function(b);
        }
                meso=(a+b)/2;
    		
    			 while(my_function(meso)!=0 || ((b-a)>e) )
        		{	
        	               fm=my_function(meso);
	 	  fa=my_function(a);			               fb=my_function(b);
	 				
	        		if((fa>0)&&(fm>0) || (fa<0)&&(fm<0))
		        		{
			        		b=meso;
			        	}	
		        		else 
		        		{
			        		a=meso;
		        		}
		        		meso=(a+b)/2;
		      }
		      
		      	if(my_function(meso)==0)
		     		 printf("%lf IS THE ROOT OF THE FUNCTION F(X)",meso);
		        	else if(((b-a)<e))
		        	printf("THE ROOT APPROXIMATIVE IS %lf",meso);
return 0;
}

double my_function(double x)
{   double fx;
    fx=x*x*x+4*x*x-10;
return fx;
}