[main.{c,h}] Let's put some safety into this code! xD

Makefile

@@ -23,4 +23,8 @@ install:
 
 uninstall:
 	rm -f ${DESTDIR}usr/bin/${TARGET}
-	rm -f ${DESTDIR}usr/share/licenses/${TARGET}/LICENSE
+	rm -f ${DESTDIR}usr/share/licenses/${TARGET}/LICENSE
+
+test:
+	@echo -n "Does input \"3.68 120 30d\" gives 317.95? "
+	@test "${shell ./kwh-cost 3.68 120 30d}" = "317.95" && { echo -e "\e[32mYES\e[0m"; } || { echo -e "\e[31mNO\e[0m"; }

src/main.c

@@ -4,7 +4,7 @@
 
 #include "main.h"
 
-int main(int argc, char **argv) {
+int main(int const argc, const char * const * const argv) {
     price_t price;
     wattage_t wattage;
     interval_t interval = 0;
@@ -23,7 +23,7 @@ int main(int argc, char **argv) {
     return 0;
 }
 
-int parse_arguments(int argc, char **argv, price_t *price, wattage_t *wattage, interval_t *interval) {
+int parse_arguments(const int argc, const char *const *const argv, price_t *const price, wattage_t *const wattage, interval_t *const interval) {
     if (argc < 2) return 1;
 
     for (int i = 1, pos = 0; i < argc; ++i)
@@ -46,7 +46,7 @@ int parse_arguments(int argc, char **argv, price_t *price, wattage_t *wattage, i
     return 0;
 }
 
-inline interval_t interval_to_seconds(char *interval) {
+inline interval_t interval_to_seconds(const char * const interval) {
     interval_t intrvl = (interval_t)atol(interval);
 
     switch (interval[strlen(interval) - 1]) {
@@ -64,7 +64,7 @@ inline interval_t interval_to_seconds(char *interval) {
     }
 }
 
-inline price_t to_wattspersecond(price_t price) {
+inline price_t to_wattspersecond(const price_t price) {
     return price / 1000.f / 3600.f;
 }
 

src/main.h

@@ -7,10 +7,10 @@ typedef long double   price_t;
 typedef long double   wattage_t;
 typedef unsigned long interval_t;
 
-int parse_arguments(int argc, char **argv, price_t *price, wattage_t *wattage, interval_t *interval);
+int parse_arguments(const int argc, const char *const *const argv, price_t *const price, wattage_t *const wattage, interval_t *const interval);
 
-inline interval_t interval_to_seconds(char *interval);
-inline price_t    to_wattspersecond(price_t price);
+inline interval_t interval_to_seconds(const char * const interval);
+inline price_t    to_wattspersecond(const price_t price);
 
 inline void print_version();
 inline void print_usage();