Initial data commit

Task/Parsing-RPN-calculator-algorithm/FreeBASIC/parsing-rpn-calculator-algorithm.basic

@@ -0,0 +1,81 @@
+#define NULL 0
+
+type node
+    'implement the stack as a linked list
+    n as double
+    p as node ptr
+end type
+
+function spctok( byref s as string ) as string
+    'returns everything in the string up to the first space
+    'modifies the original string to begin at the fist non-space char after the first space
+    dim as string r
+    dim as double i = 1
+    while mid(s,i,1)<>" " and i<=len(s)
+        r += mid(s,i,1)
+        i+=1
+    wend
+    do
+        i+=1
+    loop until mid(s,i,1)<>" " or i >= len(s)
+    s = right(s,len(s)-i+1)
+    return r
+end function
+
+sub print_stack( byval S as node ptr )
+    'display everything on the stack
+    print "Stack   <---   ";
+    while S->p <> NULL
+        S = S->p
+        print S->n;"   ";
+    wend
+    print
+end sub
+
+sub push( byval S as node ptr, v as double )
+    'push a value onto the stack
+    dim as node ptr x
+    x = allocate(sizeof(node))
+    x->n = v
+    x->p = S->p
+    S->p = x
+end sub
+
+function pop( byval S as node ptr ) as double
+    'pop a value from the stack
+    if s->P = NULL then return -99999
+    dim as double r = S->p->n
+    dim as node ptr junk = S->p
+    S->p = S->p->p
+    deallocate(junk)
+    return r
+end function
+
+dim as string s = "3 4 2 * 1 5 - 2 3 ^ ^ / +", c
+dim as node StackHead
+
+while len(s) > 0
+    c = spctok(s)
+    print "Token: ";c;"  ";
+    select case c
+        case "+"
+            push(@StackHead, pop(@StackHead) + pop(@StackHead))
+            print "Operation +     ";
+        case "-"
+            push(@StackHead, -(pop(@StackHead) - pop(@StackHead)))
+            print "Operation -     ";
+        case "/"
+            push(@StackHead, 1./(pop(@StackHead) / pop(@StackHead)))
+            print "Operation /     ";
+        case "*"
+            push(@StackHead, pop(@StackHead) * pop(@StackHead))
+            print "Operation *     ";
+        case "^"
+            push(@StackHead, pop(@StackHead) ^ pop(@StackHead))
+            print "Operation ^     ";
+        case else
+            push(@StackHead, val(c))
+            print "Operation push  ";
+    end select
+    print_stack(@StackHead)
+wend