add (FROM and TO)_FIRST_NUMBER_VOID flags

 * add decrement_number_string()
 * add (FROM and TO)_FIRST_NUMBER_VOID flags

Signed-off-by: Daniel Santos <dacs.git@brilhante.top>

1 files changed, 39 insertions, 0 deletions

diff --git a/numericx.c b/numericx.c
index c5eef26..07dd870 100644
--- a/numericx.c
+++ b/numericx.c
@@ -76,6 +76,28 @@ increment(numeral_ptr* numeral, char* num_first, char* num_last)
 		++(numeral->symbol);
 }
 
+void
+decrement_number_string(char* number, char* first_number, char* last_number, char* numeral_system)
+{
+	while( *number == *first_number )
+	{
+		*number = *last_number;
+		++number;
+	}
+
+	if( *number == '\0' )
+	{
+		*(--number) = '\0';
+	}
+	else
+	{
+		while( !(*numeral_system == *number) )
+			++numeral_system;
+
+		*number = *(--numeral_system);
+	}
+}
+
 bool
 is_the_same(numeral_ptr* numeral, char* number_arg)
 {
@@ -172,6 +194,23 @@ main(int argc, char* argv[])
 	numeral_ptr* counting = new_digit(NULL, from_first);
 	numeral_ptr* result = new_digit(NULL, to_first);
 
+	/* first number void */
+	if( !(FROM_FIRST_NUMBER_VOID && TO_FIRST_NUMBER_VOID) )
+	{
+		if( FROM_FIRST_NUMBER_VOID )
+		{
+			if( strlen(number) == 1 && *number == *from_first )
+			{
+				fprintf(stderr, "error: unrepresentable void number\n");
+				exit(EXIT_FAILURE);
+			}
+			decrement_number_string(number, from_first, from_last, from_first);
+		}
+
+		if( TO_FIRST_NUMBER_VOID )
+			increment(result, to_first, to_last);
+	}
+
 	/* increments until it finishes */
 	while( !is_the_same(counting, number) )
 	{