From b782b3f9b677d2fcfdbf79a30b3fd4e8a0002aec Mon Sep 17 00:00:00 2001
From: Martin Ashby <martin@ashbysoft.com>
Date: Sat, 11 Feb 2023 17:35:26 +0000
Subject: Exercise 5.10

---
 ex5-10.c | 113 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 113 insertions(+)
 create mode 100644 ex5-10.c

(limited to 'ex5-10.c')

diff --git a/ex5-10.c b/ex5-10.c
new file mode 100644
index 0000000..c4afccd
--- /dev/null
+++ b/ex5-10.c
@@ -0,0 +1,113 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <ctype.h>
+#include <string.h>
+
+#define NUMBER '0'
+#define MAXLINE 1000
+#define MAXVAL 100
+
+int getop(char[]);
+
+void push(double);
+double pop(void);
+void clear(void);
+double peek(void);
+
+// Naïve implementation of remainder operation
+double frem(double f1, double f2) {
+    return f1 - (f2 * (int)(f1 / f2));
+}
+
+/**
+ * Reverse polish notation calculator
+ */
+int main(int argc, char* argv[]) {
+    if (argc <= 1) {
+        fprintf(stderr, "Usage: rpol EXPR...");
+        return 1;
+    }
+    argv++; // Skip program name
+    double op2;
+    for (; *argv != NULL; argv++) {
+        char* tok = *argv;
+        int type = getop(tok);
+        switch (type) {
+            case NUMBER:
+                push(atof(tok));
+                break;
+            case '+':
+                push(pop() + pop());
+                break;
+            case '*':
+                push(pop() * pop());
+                break;
+            case '-':
+                op2 = pop();
+                push(pop() - op2);
+                break;
+            case '/':
+                op2 = pop();
+                if (op2 != 0.0)
+                    push(pop() / op2);
+                else
+                    printf("error: zero division attempted!\n");
+                break;
+            case '%':
+                op2 = pop();
+                if (op2 != 0.0) 
+                    push(frem(pop(), op2));
+                else 
+                    printf("error: zero division attempted!\n");
+                break;
+            case '~':
+                clear();
+                break;
+            default:
+                printf("unknown command %s\n", tok); // Just ignore it?
+                break;
+        }
+    }
+
+    printf("\t%.8g\n", pop());
+    return 0;
+}
+
+int sp; // Stack position
+double val[MAXVAL]; // Value stack
+void push(double f) {
+    if (sp < MAXVAL) {
+        val[sp++] = f;
+    } else {
+        printf("error, stack full\n");
+    }
+}
+
+double pop(void) {
+    if (sp >= 0) {
+        return val[--sp];
+    } else {
+        printf("error, empty stack\n");
+        return 0.0;
+    }
+}
+
+double peek(void) {
+    if (sp >= 0) {
+        return val[sp-1];
+    } else {
+        printf("error, empty stack\n");
+        return 0.0;
+    }   
+}
+
+void clear(void) {
+    sp = 0;
+}
+
+int getop(char s[]) {
+    char c = s[0];
+    if (!isdigit(c) && c != '.') 
+        return c;
+    return NUMBER;
+}
-- 
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