[Nognir]

Hey guys, I've got a similar problem here. I'm trying to make a program to calculate a polyonym but I'm getting an error. Here's the code:

#include <stdio.h>
#include <stdlib.h>
#define epsilon = 0.0001;

int p_grade, p_2nd, p_1st, p_zero, i, *p;
float x1,x2,x_0, err, x_mid;

float force (float x, int y)
{
	int i, j=1;
	for (i=1; i < y; i++) j*=x;
	return j;
}

float f (int x)			/*Ορισμός συνάρτησης πολυωνύμου*/
{
	int i, j=0;
	for (i=0; i<p_grade; i++)
	j += p[i]*force(x, p_grade);
	return j;
}								/*Τέλος ορισμού*/
float root (float a, float b)
{
	float f1, f_mid, x_mid, err;
	f1 = f(a);
	if (f(f1*(f(b)))>0) err = 1.0;
		else
			{
				err = 0;
				x_mid = (a+b)/2;
				while (abs(a - x_mid) > epsilon)
					{
						f_mid = f(x_mid);
						if ((f1 * f_mid) <= 0) b = x_mid;
							else
							{
								a = x_mid; f1 = f_mid;
							}
						x_mid = (a+b)/2;
					}
			}	return x_mid;
}
void main()
{
	printf("ΒΑΘΜΟΣ ΠΟΛΥΩΝΥΜΟΥ?:");  scanf("%d", &p_grade);	/* Εισαγωγή των δεδομένων της άσκησης*/
	p = (int *) malloc(p_grade * sizeof (int));
	if (p == NULL)
	    {
	    
	    }
	else
	    {
	    
	    }
	for (i = p_grade; i >= 0; i--) {printf("ΣΥΝΤΕΛΕΣΤΗΣ ΟΡΟΥ i?:"); scanf("%d", &p[i]);}

	printf("Η ΤΙΜΗ Χ1 είναι?:"); 	scanf("%f", &x1);
	printf("Η ΤΙΜΗ Χ2 είναι?:"); 	scanf("%f", &x2); 	/*Τέλος της εισαγωγής*/
	free(p);
}

I get that output:

 gcc -O3 ask3.c
ask3.c: In function ‘root’:
ask3.c:31: error: expected expression before ‘=’ token
ask3.c: In function ‘main’:
ask3.c:44: warning: return type of ‘main’ is not ‘int’

Any help here? I'd be grateful