Revert "Refactor currencyExchange"

This reverts commit 7236756d50.

src/currencyExchange.c

@@ -1,18 +1,20 @@
 #include "currencyExchange.h"
 
-#define NUM_CURRENCIES 4
+float convert(float euro, int newCurrencyCode) {
+    switch(newCurrencyCode) {
+        case CURRENCY_CODE_USD:
+            return ( euro * USD_RATE_OF_ONE_EURO );
 
-float exchangeRates[NUM_CURRENCIES] = {
-    USD_RATE_OF_ONE_EURO,
-    GBP_RATE_OF_ONE_EURO,
-    JAPANESE_YEN_RATE_OF_ONE_EURO,
-    CHINESE_YUAN_RATE_OF_ONE_EURO
-};
+        case CURRENCY_CODE_GBP:
+            return ( euro * GBP_RATE_OF_ONE_EURO );
+
+        case CURRENCY_CODE_JAPANESE_YEN:
+            return ( euro * JAPANESE_YEN_RATE_OF_ONE_EURO );
+
+        case CURRENCY_CODE_CHINESE_YUAN:
+            return ( euro * CHINESE_YUAN_RATE_OF_ONE_EURO );
 
-float convert(float euro, int newCurrencyCode) {
-    if (newCurrencyCode >= 0 && newCurrencyCode < NUM_CURRENCIES) {
-        return euro * exchangeRates[newCurrencyCode];
     }
     
     return -1;
-}
+}