C - GetFloat: The floating-point analog of GetInt

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/*
 * GetFloat: The floating-point analog of GetInt.
 *
 * GetFloat.c - by FreeMan
 */

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

#define BUFFERLENGTH 100

int GetCh(void);
void UngetCh(int);

int buf[BUFFERLENGTH];
int nfp = 0;

void ViewBuffer(void)
{
	int i;
	printf("\nbuffer:\n");
	for (i = nfp - 1; i >= 0; i--)
	{
		printf("%d\n", buf[i]);
	}
}

int GetCh(void)
{
	return (nfp > 0) ? buf[--nfp] : getchar();
}

void UngetCh(int c)
{
	if (nfp < BUFFERLENGTH)
	{
		buf[nfp++] = c;
	}
	else
	{
		printf("error: ungetch buffer overflow\n");
	}
}

int GetFloat(float *pn)
{
	int c, i, sign;
	while (isspace(c = getchar()))
		;
	if (!isdigit(c) && c != EOF && c != '+' && c != '-')
	{
		UngetCh(c);
		return 0;
	}
	sign = (c == '-') ? -1 : 1;
	if (c == '+' || c == '-')
	{
		c = GetCh();
		if (!isdigit(c))
		{
			UngetCh(sign == -1 ? '-' : '+');
			return 0;
		}
	}
	for (*pn = 0; isdigit(c); c = getch())
	{
		*pn = *pn * 10 + (c - '0');
	}
	if (c == '.')
	{
		c = GetCh();
		for (i = 1; isdigit(c); c = GetCh(), i++)
		{
			*pn += (c - '0') / pow(10, i);
		}
	}
	*pn *= sign;
	if (c != EOF)
	{
		UngetCh(c);
	}
	return c;
}

int main()
{
	int retval;
	float x, *px;
	px = &x;
	retval = GetFloat(px);
	printf("retval = %d, x = %.3f\n", retval, x);
	ViewBuffer();
	return 0;
}

// Input:
/*
   -123.456
*/

// Output:
/*
retval = 10, x = -123.456

buffer:
10

*/