From 4d95f4515b958aeb13dc11b2e9304184849273fd Mon Sep 17 00:00:00 2001
From: Tibor Bizjak <tibor.bizjak@gmail.com>
Date: Sat, 8 Jul 2023 16:37:54 +0200
Subject: [PATCH] k&r 04-03: rewrote calculator, added modulo and negative
 numbers

---
 k&r/04-funcs-and-prog-struct/04-calc.c | 120 +++++++++++++++++++++++++
 1 file changed, 120 insertions(+)
 create mode 100644 k&r/04-funcs-and-prog-struct/04-calc.c

diff --git a/k&r/04-funcs-and-prog-struct/04-calc.c b/k&r/04-funcs-and-prog-struct/04-calc.c
new file mode 100644
index 0000000..b564b2f
--- /dev/null
+++ b/k&r/04-funcs-and-prog-struct/04-calc.c
@@ -0,0 +1,120 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+
+#define printerr(format, ...) printf("error: " format "\n", ##__VA_ARGS__)
+void push(double x);
+double pop(void);
+int stack_len(void);
+
+/* --------- ERROR MESSAGES */
+#define ZERODIV_ERR "zero divisor"
+
+
+/* --------- CALCULATOR FUNCTIONS */
+/* commutative operator application */
+#define COMM_OP(OP) push(pop() OP pop()) 
+/* non-commutative operator application */
+#define NONC_OP(OP, T, ...) \
+    do { T op2 = pop(); __VA_ARGS__ push(((T) pop()) OP op2); } while (0)
+/* nonzero second operand operator application */
+#define NONZ_OP(OP, T) \
+    NONC_OP(OP, T, if (!op2) printerr(ZERODIV_ERR); else)
+
+#define FUNCTIONS \
+    X(+, COMM_OP) \
+    X(*, COMM_OP) \
+    X(-, NONC_OP, double) \
+    X(/, NONZ_OP, double) \
+    X(%, NONZ_OP, int) 
+
+
+
+#define MAXTOKEN 100
+int gettoken(char *token, int max_t);
+
+/* reverse Polish calculator */
+int main()
+{
+    char token[MAXTOKEN + 1];
+    double op2;
+    int t_len;
+
+    while (t_len = gettoken(token, MAXTOKEN)) {
+        if (t_len < 0) 
+            printf("\t%g\n",  pop());
+        else
+    #define X(F, APPLY, ...) \
+        if (!strcmp(#F, token)) \
+            APPLY(F, ##__VA_ARGS__); \
+        else
+        FUNCTIONS
+    #undef X
+        push(atof(token));
+    }
+    printf("%g\n", pop());
+
+    return 0;
+}
+
+/* -------- PARSING FUNCTIONS */
+#include <ctype.h> 
+
+#define BLANK ' '
+
+/* gettoken: get next space delimited token from input
+ * return token length, -1 on newline and 0 on EOF */
+int gettoken(char *token, int t_max) 
+{
+
+    static int c = BLANK;
+    
+    while (isspace(c) && c != '\n') /* remove leading whitespace */
+        c = getchar();
+
+    if (c == '\n') { /* newline is a token */
+        c = BLANK;
+        return -1;
+    }
+
+    /* fetch token */
+    int i;
+    for (i = 0; i < t_max && c != EOF && !isspace(c); c = getchar(), i++) 
+        token[i] = c;
+
+    token[i] = '\0';
+    return i;
+}
+
+/* ------ GLOBAL STACK */
+#define MAXVAL 100 /* maximum depth of val stack */
+
+int sp = 0;
+double val[MAXVAL];
+
+int stack_len()
+{
+    return sp;
+}
+
+/* push: push f onto value stack */
+void push(double f)
+{
+    if (sp < MAXVAL)
+        val[sp++] = f;
+    else
+        printf("error: stack full, can't push %g\n", f);
+
+}
+
+/* pop: pop and return top value from stack */
+double pop(void)
+{
+    if (sp)
+        return val[--sp];
+    printf("error: stack empty\n");
+    return 0.0;
+}
+
+