1 files changed, 133 insertions, 0 deletions
diff --git a/5.6.4.c b/5.6.4.c
new file mode 100644
index 0000000..bec00f1
--- /dev/null
+++ b/5.6.4.c
@@ -0,0 +1,133 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <ctype.h>
+#include <math.h>
+
+#define MAXOP 100
+#define NUMBER_SIG '0'
+
+double pop(void);
+void push(double f);
+char getop(char str[]);
+
+int 
+main(void)
+{
+  char str[MAXOP];
+  char type;
+  double op2;
+
+  while ((type = getop(str)) != EOF) {
+    switch (type) {
+      case NUMBER_SIG :
+        push(atof(str));
+        break;
+      case '+' :
+        push(pop() + pop());
+        break;
+      case '*' :
+        push(pop() * pop());
+        break;
+      case '-' :
+        op2 = pop();
+        push(pop() - op2);
+        break;
+      case '/' :
+        if ((op2 = pop()) == 0.0)
+          printf("Err: deviser cant be zero\n");
+        else 
+          push(pop() / op2);
+
+        break;
+      case '%' :
+        op2 = pop();
+        if (op2 != 0)
+          push(fmod(pop(), op2));
+        else 
+          printf("Err: deviser cant be zero\n");
+
+        break;
+      case '\n' :
+        printf("%.8g\n", pop());
+        break;
+      default :
+        printf("Err: unknown command\n");
+    }
+  }
+
+  return 0;
+}
+
+#define MAXVAL 100
+double val[MAXVAL];
+int sp = 0;
+
+double 
+pop(void)
+{
+  if (sp > 0)
+    return val[--sp];
+  else {
+    printf("Err: stack empty\n");
+    return 0.0;
+  }
+}
+
+void
+push(double f)
+{
+  if (sp < MAXVAL)
+    val[sp++] = f;
+  else
+    printf("Err: stack is full\n");
+}
+
+char getch(void);
+void ungetch(char input);
+
+char 
+getop(char str[])
+{
+  char input, *str_og;
+
+  str_og = str;
+
+  /* ignore blanks */
+  while (isblank(input = *str = getch()));
+  
+  /* return operator */
+  if (!isdigit(input) && input != '.')
+    return input;
+
+  /* collect digits*/
+  while (str - str_og < MAXOP && (isdigit(input=getch()) || input == '.'))
+    *++str = input;
+
+  *++str = '\0';
+
+  if (input != EOF)
+    ungetch(input);
+
+  return NUMBER_SIG;
+}
+
+#define MAXBUFF 100
+char buff[MAXBUFF];
+int bp = 0;
+
+char
+getch(void)
+{
+  return (bp > 0) ? buff[--bp] : getchar();
+}
+
+void
+ungetch(char input)
+{
+  if (bp < MAXBUFF)
+    buff[bp++] = input;
+  else {
+    printf("Err: buffer full\n");
+  }
+}
+