gistfile1.c

#include <stdio.h>
#include <math.h>
#include <float.h>

#define EPSILON 0.01

float func(float x)
{
  return powf(x, 4) + 5 * x - 7;
}

void main(void)
{
	float a = 0 + EPSILON;
	float b = FLT_MAX;
	float c = 0;

	while(fabs(a - b) >= EPSILON)
	{
		c = (a + b) / 2;

		if(func(b) * func(c) < 0)
			a = c;
		else
			b = c;
	}

	printf("%10.10f\n", c);

	return 0;
}