add problem 13 and test function

Author: supercoderhawk

C/1-50/13-Roman-to-Integer.c

@@ -0,0 +1,43 @@
+/*
+ * Given a roman numeral, convert it to an integer.
+
+ * Input is guaranteed to be within the range from 1 to 3999.
+ * Created by supercoderx on 2017/8/11.
+ */
+#include 
+
+int romanToInt(char *s) {
+    char chs[] = "IVXLCDM";
+    int chsNum[] = {1, 5, 10, 50, 100, 500, 1000}, len = 0, chsLen = 7, id, prevId, res = 0;
+
+    char *ch = s;
+    while (*ch != '\0') {
+        ch++;
+        len++;
+    }
+
+    for (int i = len - 1; i >= 0; i--) {
+        for (int j = 0; j < chsLen; j++)
+            if (s[i] == chs[j]) {
+                id = j;
+                break;
+            }
+        if (i == len - 1) {
+            res = chsNum[id];
+            prevId = id;
+        } else {
+            if (chsNum[id] < chsNum[prevId])
+                res -= chsNum[id];
+            else
+                res += chsNum[id];
+            prevId = id;
+        }
+    }
+
+    return res;
+}
+
+void testRomanToInt() {
+    char *s1 = "IV";
+    printf("%d", romanToInt(s1));
+}