Initial data commit

Task/Parsing-RPN-calculator-algorithm/C/parsing-rpn-calculator-algorithm-2.c

@@ -0,0 +1,53 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <ctype.h>
+#include <string.h>
+#include <math.h>
+
+#define die(msg) fprintf(stderr, msg"\n"), abort();
+double get(const char *s, const char *e, char **new_e)
+{
+	const char *t;
+	double a, b;
+
+	for (e--; e >= s && isspace(*e); e--);
+	for (t = e; t > s && !isspace(t[-1]); t--);
+
+	if (t < s) die("underflow");
+
+#define get2(expr) b = get(s, t, (char **)&t), a = get(s, t, (char **)&t), a = expr
+	a = strtod(t, (char **)&e);
+	if (e <= t) {
+		if	(t[0] == '+') get2(a + b);
+		else if (t[0] == '-') get2(a - b);
+		else if (t[0] == '*') get2(a * b);
+		else if (t[0] == '/') get2(a / b);
+		else if (t[0] == '^') get2(pow(a, b));
+		else {
+			fprintf(stderr, "'%c': ", t[0]);
+			die("unknown token");
+		}
+	}
+#undef get2
+
+	*(const char **)new_e = t;
+	return a;
+}
+
+double rpn(const char *s)
+{
+	const char *e = s + strlen(s);
+	double v = get(s, e, (char**)&e);
+
+	while (e > s && isspace(e[-1])) e--;
+	if (e == s) return v;
+
+	fprintf(stderr, "\"%.*s\": ", e - s, s);
+	die("front garbage");
+}
+
+int main(void)
+{
+	printf("%g\n", rpn("3 4 2 * 1 5 - 2 3 ^ ^ / +"));
+	return 0;
+}