four/op.c


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#include <stdio.h>

#define MAXVAL 100
#define NUMBER '0'

int sp = 0;
double val[MAXVAL];

void
push(double f)
{
	if (sp < MAXVAL) {
		val[sp++] = f;
	} else {
		printf("error: stack full, can't push %g\n", f);
	}
}

double
pop(void)
{
	if (sp > 0) {
		return val[--sp];
	} else {
		printf("error: stack empty\n");
		return 0.0;
	}
}

double
peek()
{
	return val[sp - 1];
}

void
clear()
{
	while (sp) {
		val[sp--] = 0;
	}
}