Refactoring: Remove useless code and update constant names

src/currencyExchange.c

@@ -1,25 +1,13 @@
 #include "currencyExchange.h"
 
-float toUSD(float euro) {
-
-    float USD = euro * CURRENT_USD_RATE_OF_ONE_EURO;
-
-    return USD;
-}
-
-float toGBP(float euro) {
-
-    float GBP = euro * CURRENT_GBP_RATE_OF_ONE_EURO;
-
-    return GBP;
-}
-
 float convert(float euro, int newCurrencyCode) {
     switch(newCurrencyCode) {
-        case 1:
-            return ( euro * CURRENT_USD_RATE_OF_ONE_EURO );
-        case 2:
-            return ( euro * CURRENT_GBP_RATE_OF_ONE_EURO );
+        case CURRENCY_CODE_USD:
+            return ( euro * USD_RATE_OF_ONE_EURO );
+
+        case CURRENCY_CODE_GBP:
+            return ( euro * GBP_RATE_OF_ONE_EURO );
     }
+    
     return -1;
 }