tasks a-s

Task/Roman-numerals-Decode/C/roman-numerals-decode.c

@@ -0,0 +1,47 @@
+#include <stdio.h>
+
+int digits[26] = { 0, 0, 100, 500, 0, 0, 0, 0, 1, 1, 0, 50, 1000, 0, 0, 0, 0, 0, 0, 0, 5, 5, 0, 10, 0, 0 };
+
+/* assuming ASCII, do upper case and get index in alphabet. could also be
+        inline int VALUE(char x) { return digits [ (~0x20 & x) - 'A' ]; }
+   if you think macros are evil */
+#define VALUE(x) digits[(~0x20 & (x)) - 'A']
+
+int decode(const char * roman)
+{
+        const char *bigger;
+        int current;
+        int arabic = 0;
+        while (*roman != '\0') {
+                current = VALUE(*roman);
+                /*      if (!current) return -1;
+                        note: -1 can be used as error code; Romans didn't even have zero
+                */
+                bigger = roman;
+
+                /* look for a larger digit, like IV or XM */
+                while (VALUE(*bigger) <= current && *++bigger != '\0');
+
+                if (*bigger == '\0')
+                        arabic += current;
+                else {
+                        arabic += VALUE(*bigger);
+                        while (roman < bigger)
+                                arabic -= VALUE(* (roman++) );
+                }
+
+                roman ++;
+        }
+        return arabic;
+}
+
+int main()
+{
+        const char * romans[] = { "MCmxC", "MMVIII", "MDClXVI", "MCXLUJ" };
+        int i;
+
+        for (i = 0; i < 4; i++)
+                printf("%s\t%d\n", romans[i], decode(romans[i]));
+
+        return 0;
+}