Check if number belongs to numerical system

* add is_valid_number()
 * check if number belongs to the 'from' numerical system

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

numericx.c

@@ -177,6 +177,22 @@ reverse_string(char* string)
 	}
 }
 
+bool is_valid_number(char* numeral_system, char *number)
+{
+	/*
+	if( *number == '-' || *number == '+' )
+		++number;
+	*/
+	while( !(*number == '\0') )
+	{
+		if( strchr(numeral_system, *number) == NULL )
+			return false;
+		++number;
+	}
+
+	return true;
+}
+
 int
 main(int argc, char* argv[])
 {
@@ -199,6 +215,13 @@ main(int argc, char* argv[])
 	/* Number variables to be converted */
 	char* number = argv[1];
 
+	/* Check if number belongs to it's numerical system */
+	if( !is_valid_number(from, number) )
+	{
+		fprintf(stderr, "error: %s.\n", strerror(EDOM));
+		exit(EDOM);
+	}
+
 	/* _first and _last variables */
 	char* from_first = from;
 	char* from_last = from + (strlen(from) - 1);