[Dana] (Simple) Calculator Program (#65)

* [Dana] (Simple) Calculator Program

The program takes reads the input line by line and
on each line it expects an integer followed by and operator and then
another integer, any other character among them is ignored.
If the input is valid it outputs the operation's result otherwise it
fails on that line with a message "Invalid"

There is also a sample input and output for the program

* [Dana] Calculator Program, better comments

Author: kkgiorgos

dana/programs/calculator.dana

@@ -0,0 +1,119 @@
+def main
+    # Helper Function
+
+    def is_digit is byte: c as byte
+        if '0' <= c and c <= '9':   return: true
+        else:                       return: false
+
+    def is_operator is byte: c as byte
+        if c = '+' or c = '-' or c = '*' or c = '/':
+            return: true
+        else:
+            return false
+
+    (*
+        Conversion from part of a string to an int
+        [from, to)
+    *)
+    def string_to_int is int: s as byte[], from to as int
+        var i res pow is int
+
+        res := 0
+        pow := 1
+
+        i := to - 1
+        loop:
+            if i < from: break
+            res := res + pow * extend(s[i] - '0')
+            pow := pow * 10
+            i := i - 1
+
+        return: res
+
+    (*
+        Simple Calculator
+
+        Input: lines of the following form:
+        <Num1> <Op> <Num2>
+        where <NumX> is a positive integer
+        and <Op> is one of +, -, *, /
+        Any other characters among them get ignored.
+
+        Output: lines with the results
+        or a message "Invalid" in case of failure
+    *)
+
+    var buf is byte[256]
+    var idx len start end a b is int
+    var op is byte
+
+    loop lines:
+        readString: 256, buf
+
+        # Stop if we got nothing
+        len := strlen(buf)
+        if len = 0: break: lines
+
+        idx := 0
+
+        loop a_start:
+            if idx == len:
+                writeString: "Invalid\n"
+                continue: lines
+            elif is_number(buf[idx]):
+                break: a_start
+            idx := idx + 1
+        start := idx;
+
+        loop a_end:
+            if idx == len:
+                writeString: "Invalid\n"
+                continue: lines
+            elif not is_number(buf[idx]):
+                break: a_end
+            idx := idx + 1
+        end := idx;
+
+        a := string_to_int(buff, start, end);
+
+        loop op_detect:
+            if idx == len:
+                writeString: "Invalid\n"
+                continue: lines
+            elif is_operator(buf[idx]):
+                break: op_detect
+            idx := idx + 1
+        op := buf[idx]
+
+        loop b_start:
+            if idx == len:
+                writeString: "Invalid\n"
+                continue: lines
+            elif is_number(buf[idx]):
+                break: b_start
+            idx := idx + 1
+        start := idx;
+
+        loop b_end:
+            if idx == len or not is_number(buf[idx]):
+                break: b_end
+            idx := idx + 1
+        end := idx;
+
+        b := string_to_int(buff, start, end);
+
+        # We have finished parsing now we can calculate
+
+        if op = '+':
+            writeInteger: a + b
+        elif op = '-':
+            writeInteger: a - b
+        elif op = '*':
+            writeInteger: a * b
+        elif op = '/':
+            writeInteger: a / b
+        else:
+            writeString: "Invalid\n"
+
+    exit
+

dana/programs/calculator.input

@@ -0,0 +1,11 @@
+1+2
+4-3
+5*2
+100/4
+25 + 10
+  10 *   3  dsfdfadf
+asdf 5sdf -adfd2
+5-
+35+
++7
+2345 _ 2342

dana/programs/calculator.output

@@ -0,0 +1,11 @@
+3
+1
+10
+25
+35
+30
+3
+Invalid
+Invalid
+Invalid
+Invalid