4.11

1 files changed, 152 insertions, 0 deletions

diff --git a/4/11.c b/4/11.c
new file mode 100644
index 0000000..bf224c7
--- /dev/null
+++ b/4/11.c
@@ -0,0 +1,152 @@
+#include <ctype.h>
+#include <math.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#define MAXOP 100
+#define HEIGHT 1000
+
+#define NUM '0'
+#define FUN '1'
+#define VAR '2'
+
+#define INDEX(x) (x <= 'Z' ? x - 'A' : x - 71) /* index of the variable */
+
+char var[52];
+double lout = 0.0;
+
+int getop(char[]);
+void push(double);
+double pop();
+double peek();
+void clear();
+
+/* Stack based reverse Polish notation calculator without ungetch()
+      - single uppercase and lowercase characters are variables (syntax 2 A =);
+      - special variable LOUT for the last printed value.
+      - mathematical functions: sin, cos, tan, exp, pow.
+      - custom functions: swp (swap top 2 values), dup (duplicate last value),
+        top (peek at the stack top), cls (clear stack).
+      - operators: +, -, *, /, % and =.
+      - press enter to print the value at the top of the stack.
+ */
+int main(int argc, char *argv[]) {
+  int type;
+  double op1, op2;
+  char s[MAXOP];
+
+  while ((type = getop(s)) != 0) {
+    switch (type) {
+    case NUM:
+      push(atof(s));
+      break;
+    case '+':
+      op1 = pop();
+      op2 = pop();
+      push(op1 + op2);
+      break;
+    case '-':
+      op2 = pop();
+      op1 = pop();
+      push(op1 - op2);
+      break;
+    case '*':
+      op2 = pop();
+      op1 = pop();
+      push(op1 * op2);
+      break;
+    case '/':
+      op2 = pop();
+      op1 = pop();
+      if (op1 == 0.0)
+        printf("error: division by zero\n");
+      else
+        push((double)op1 / op2);
+      break;
+    case '%':
+      op2 = pop();
+      op1 = pop();
+      if (op2 == 0.0)
+        printf("error: division by zero\n");
+      else
+        push((int)op1 % (int)op2);
+      break;
+    case '=':
+      var[INDEX(s[0])] = pop();
+      break;
+    case VAR:
+      if (strcmp("LOUT", s) == 0)
+        push(lout);
+      else
+        push(var[INDEX(s[0])]);
+      break;
+    case FUN:
+      if (strcmp("sin", s) == 0)
+        push(sin(pop()));
+      else if (strcmp("cos", s) == 0)
+        push(cos(pop()));
+      else if (strcmp("tan", s) == 0)
+        push(tan(pop()));
+      else if (strcmp("exp", s) == 0)
+        push(exp(pop()));
+      else if (strcmp("pow", s) == 0)
+        push(pow(pop(), pop()));
+      else if (strcmp("cls", s) == 0)
+        clear();
+      else if (strcmp("top", s) == 0) {
+        lout = peek();
+        printf("\t%.8g\n", lout);
+      } else if (strcmp("swp", s) == 0) {
+        op2 = pop();
+        op1 = pop();
+        push(op2);
+        push(op1);
+      } else if (strcmp("dup", s) == 0)
+        push(peek());
+      else
+        printf("error: unknown function %s\n", s);
+      break;
+    case '\n':
+      lout = pop();
+      printf("\t%.8g\n", lout);
+      break;
+    default:
+      printf("error: unknown command %s\n", s);
+    }
+  }
+  return 0;
+}
+
+int sp = 0;
+double stack[HEIGHT];
+
+void push(double f) {
+  if (sp < HEIGHT)
+    stack[sp++] = f;
+  else
+    printf("error: stack empty\n");
+}
+
+double pop() {
+  if (sp > 0)
+    return stack[--sp];
+  else {
+    printf("error: stack empty\n");
+    return 0.0;
+  }
+}
+
+double peek() {
+  if (sp > 0)
+    return stack[sp - 1];
+  else {
+    printf("error: stack empty\n");
+    return 0.0;
+  }
+}
+
+void clear() {
+  for (; sp > 0; sp--)
+    ;
+}
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