Rewrite to C89 standards, preserve compatibility with old x86 machines

sccash.c

@@ -24,7 +24,8 @@ const char* currency_names[] = {"USD", "JPY", "EUR"};
 
 Currency parse_currency(const char* input) {
     char upper[4] = {0};
-    for (int i = 0; i < 3 && input[i]; i++) {
+    int i;
+    for (i = 0; i < 3 && input[i]; i++) {
         upper[i] = toupper(input[i]);
     }
     
@@ -53,8 +54,9 @@ double convert_from_usd(double usd_amount, Currency to) {
 }
 
 double convert_currency(double amount, Currency from, Currency to) {
+    double usd_amount;
     if (from == to) return amount;
-    double usd_amount = convert_to_usd(amount, from);
+    usd_amount = convert_to_usd(amount, from);
     return convert_from_usd(usd_amount, to);
 }
 
@@ -73,10 +75,11 @@ void print_table_footer(void) {
 }
 
 void print_all_conversions(double amount, Currency from) {
+    int i;
     printf("\n");
     print_table_header();
     
-    for (int i = 0; i < 3; i++) {
+    for (i = 0; i < 3; i++) {
         if (i != from) {
             Currency to = (Currency)i;
             double result = convert_currency(amount, from, to);
@@ -94,7 +97,8 @@ void print_all_conversions(double amount, Currency from) {
 
 void interactive_mode(void) {
     char from_input[10], to_input[10];
-    double amount;
+    char show_all[10];
+    double amount, result;
     Currency from, to;
     
     printf("\n=== sccash - Simple C Cash ===\n\n");
@@ -129,7 +133,7 @@ void interactive_mode(void) {
         return;
     }
     
-    double result = convert_currency(amount, from, to);
+    result = convert_currency(amount, from, to);
     
     printf("\n");
     print_table_header();
@@ -138,7 +142,6 @@ void interactive_mode(void) {
     printf("\n");
     
     printf("Show all conversions? (y/n): ");
-    char show_all[10];
     scanf("%9s", show_all);
     if (show_all[0] == 'y' || show_all[0] == 'Y') {
         print_all_conversions(amount, from);
@@ -146,6 +149,9 @@ void interactive_mode(void) {
 }
 
 void cli_mode(int argc, char* argv[]) {
+    double amount, result;
+    Currency from, to;
+    
     if (argc < 4) {
         fprintf(stderr, "Usage: %s <amount> <from> <to>\n", argv[0]);
         fprintf(stderr, "  amount: numeric value to convert\n");
@@ -156,14 +162,14 @@ void cli_mode(int argc, char* argv[]) {
         exit(1);
     }
     
-    double amount = atof(argv[1]);
+    amount = atof(argv[1]);
     if (amount <= 0) {
         fprintf(stderr, "Error: Invalid amount '%s'\n", argv[1]);
         exit(1);
     }
     
-    Currency from = parse_currency(argv[2]);
-    Currency to = parse_currency(argv[3]);
+    from = parse_currency(argv[2]);
+    to = parse_currency(argv[3]);
     
     if (from == CURRENCY_INVALID) {
         fprintf(stderr, "Error: Invalid source currency '%s'\n", argv[2]);
@@ -177,7 +183,7 @@ void cli_mode(int argc, char* argv[]) {
         exit(1);
     }
     
-    double result = convert_currency(amount, from, to);
+    result = convert_currency(amount, from, to);
     
     printf("\n");
     print_table_header();