1 files changed, 42 insertions, 0 deletions
diff --git a/four/op.c b/four/op.c
new file mode 100644
index 0000000..f8e96ed
--- /dev/null
+++ b/four/op.c
@@ -0,0 +1,42 @@
+#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;
+	}
+}