adding cs142 code

cs142/smcquay/lab04/converts.cc

@@ -0,0 +1,17 @@
+#include <iostream>
+#include <cmath>
+
+#include "converts.h"
+
+int str2int(string s) {
+    int r = 0;
+    int i = 0;
+    for(auto s_it = s.rbegin(); s_it != s.rend(); s_it++) {
+        if (*s_it == '1') {
+            r += pow(2, i);
+        }
+
+        i++;
+    }
+    return r;
+}