To make it compile with clang I added void to print_*() funcs' arguments. Also I had to remove inline specifiers because clang was throwing `undefined reference`.

LICENSE

@@ -1,6 +1,6 @@
 MIT License
 
-Copyright (c) 2021 Alexander "Arav" Andreev <me@arav.top>
+Copyright (c) 2021-2024 Alexander "Arav" Andreev <me@arav.su>
 
 Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
 

Makefile

@@ -1,29 +1,26 @@
 TARGET=kwh-cost
 
-CFLAGS=--std=c2x -O3 -Wall -Werror -Wextra -pedantic
+DESTDIR:=
+PREFIX:=/usr/local
 
-SRC_DIR=src
-OBJ_DIR=obj
+CFLAGS=--std=c99 -O3 -Wall -Werror -Wextra -pedantic
 
-DESTDIR=/
 
-.PHONY: all ${TARGET} clean install uninstall
+.PHONY: clean install uninstall test
 
-all: ${TARGET}
-
-${TARGET}: ${SRC_DIR}/main.c ${SRC_DIR}/main.h
+${TARGET}: main.c
 	${CC} ${CFLAGS} ${LDFLAGS} $< -o $@
 
 clean:
 	rm ${TARGET}
 
 install:
-	install -Dm755 ${TARGET} ${DESTDIR}usr/bin/${TARGET}
-	install -Dm644 LICENSE ${DESTDIR}usr/share/licenses/${TARGET}/LICENSE
+	install -Dm755 ${TARGET} ${DESTDIR}${PREFIX}/bin/${TARGET}
+	install -Dm644 LICENSE ${DESTDIR}${PREFIX}/share/licenses/${TARGET}/LICENSE
 
 uninstall:
-	rm -f ${DESTDIR}usr/bin/${TARGET}
-	rm -rf ${DESTDIR}usr/share/licenses/${TARGET}
+	rm -f ${DESTDIR}${PREFIX}/bin/${TARGET}
+	rm -rf ${DESTDIR}${PREFIX}/share/licenses/${TARGET}
 
 test:
 	@echo -n "Does input \"3.68 120 30d\" gives 317.95? "

PKGBUILD

@@ -1,24 +1,21 @@
-# Maintainer: Alexander "Arav" Andreev <me@arav.top>
+# Maintainer: Alexander "Arav" Andreev <me@arav.su>
 pkgname=kwh-cost
-pkgver=1.1.0
+pkgver=1.1.2
 pkgrel=1
 pkgdesc="Calculates cost of electricity."
 arch=('i686' 'x86_64' 'arm' 'armv6h' 'armv7h' 'aarch64')
-url="https://git.arav.top/Arav/kwh-cost"
+url="https://git.arav.su/Arav/kwh-cost"
 license=('MIT')
-makedepends=('git' 'gcc')
-provides=('kwh-cost')
-conflicts=('kwh-cost')
 options=('strip')
-source=('https://git.arav.top/Arav/kwh-cost/archive/1.1.0.tar.gz')
+source=("${pkgver}.tar.gz::https://git.arav.su/Arav/kwh-cost/archive/${pkgver}.tar.gz")
 md5sums=('SKIP')
 
 build() {
     cd "$srcdir/$pkgname"
-    make DESTDIR="$pkgdir/"
+    make
 }
 
 package() {
     cd "$srcdir/$pkgname"
-    make DESTDIR="$pkgdir/" install
+    make DESTDIR="$pkgdir" PREFIX="/usr" install
 }

README.md

@@ -13,7 +13,7 @@ Options are `-v, --version` to show program's version; and `-h, --help` to show
 `price` is a price per kWh. `wattage` is how many Watts being consumed. `interval` is for how long.
 
 `interval` is in seconds, but you can specify a unit. Units are the following:
-`m` for minutes; `h` for hours; and `d` for days. There could be as many `interval`s passed as you need.
+`m|M` for minutes; `h|H` for hours; and `d|D` for days. There could be as many `interval`s passed as you need.
 
 Here is an example:
 
@@ -27,10 +27,10 @@ Will give 348.29.
 
 ### Manually
 
-First run `make` to build a program, and then `make install` to copy executable in `/usr/bin/`. Later, use `make uninstall` to delete it, or just delete `/usr/bin/kwh-cost`.
+First run `make` to build a program, and then `make install` to copy executable in `/usr/local/bin/`. Later, use `make uninstall` to delete it, or just delete `/usr/local/bin/kwh-cost`.
+
+A `LICENSE` file is also being copied to `/usr/local/share/licenses/kwh-cost/LICENSE`.
 
 ### For ArchLinux
 
 You can take a [PKGBUILD](/Arav/kwh-cost/raw/branch/master/PKGBUILD) file and in a directory with it run `makepkg -i`.
-
-If you want to use a pre-built package for Arch from Releases, then install it using `pacman -U` command.

main.c

@@ -0,0 +1,107 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#define VERSION "1.1.2"
+
+typedef long double   price_t;
+typedef long double   wattage_t;
+typedef unsigned long interval_t;
+
+int parse_arguments(const int argc, const char *const *const argv,
+                    price_t *const price, wattage_t *const wattage, interval_t *const interval);
+
+interval_t interval_to_seconds(const char *const interval);
+price_t    price_kwh_to_wattsecond(const price_t price);
+
+void print_version(void);
+void print_usage(void);
+
+int main(const int argc, const char *const *const argv) {
+    price_t price;
+    wattage_t wattage;
+    interval_t interval = 0;
+
+    switch (parse_arguments(argc, argv, &price, &wattage, &interval)) {
+        case 1: print_usage(); exit(0);
+        case 2: print_version(); exit(0);
+        case 99: fputs("Unknown flag provided.\n", stderr); print_usage(); exit(1);
+    }   
+
+    printf("%.2Lf\n", (price * wattage) * interval);
+
+    return 0;
+}
+
+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)
+        if (argv[i][0] == '-') {
+            size_t l = strlen(argv[i]);
+            if (l < 2)
+                return 99;
+            if (argv[i][1] == 'h' || (argv[i][1] == '-' && l > 2 && argv[i][2] == 'h'))
+                return 1;
+            else if (argv[i][1] == 'v' || (argv[i][1] == '-' && l > 2 && argv[i][2] == 'v'))
+                return 2;
+            else
+                return 99;
+        } else if (argc < 4) {
+            return 1;
+        } else if (pos == 0) {
+            *price = price_kwh_to_wattsecond((price_t)atof(argv[i]));
+            ++pos;
+        } else if (pos == 1) {
+            *wattage = (wattage_t)atof(argv[2]);
+            ++pos;
+        } else
+            *interval += interval_to_seconds(argv[i]);
+
+    return 0;
+}
+
+interval_t interval_to_seconds(const char *const interval) {
+    interval_t intrvl = (interval_t)atol(interval);
+
+    switch (interval[strlen(interval) - 1]) {
+        case 'm':
+        case 'M':
+            return intrvl * 60;
+        case 'h':
+        case 'H':
+            return intrvl * 60 * 60;
+        case 'd':
+        case 'D':
+            return intrvl * 60 * 60 * 24;
+        default:
+            return intrvl;
+    }
+}
+
+price_t price_kwh_to_wattsecond(const price_t price) {
+    return price / 1000.f / 3600.f;
+}
+
+void print_version(void) {
+    fputs("kwh-cost Ver. " VERSION "\n"
+         "Copyright (C) 2021-2024 Alexander \"Arav\" Andreev <me@arav.su>. All rights reserved.\n"
+         "This program is distributed under the terms of MIT+NIGGER licence.\n"
+         "You can see a license for this program in /usr/share/licenses/kwh-cost/LICENSE.\n", stderr);
+}
+
+void print_usage(void) {
+    fputs("Usage: kwh-cost [OPTIONS] price wattage interval [interval ...]\n"
+         "Options:\n"
+         "  --help, -h     display this usage information.\n"
+         "  --version, -v  display program version.\n"
+         "Arguments:\n"
+         "  price     price per kWh.\n"
+         "  wattage   power usage in Watts.\n"
+         "  interval  time interval in seconds during which\n"
+         "            this much power to be constantly used.\n"
+         "            You may specify other time units such as:\n"
+         "            m'inute, h'our, d'ay. Example: 5d 3h.\n"
+         "            All given intervals will be summed up.\n", stderr);
+}

src/main.c

@@ -1,91 +0,0 @@
-#include <stdio.h>
-#include <stdlib.h>
-#include <string.h>
-
-#include "main.h"
-
-int main(const int argc, const char * const * const argv) {
-    price_t price;
-    wattage_t wattage;
-    interval_t interval = 0;
-
-    int res = parse_arguments(argc, argv, &price, &wattage, &interval);
-    if (res != 0) {
-        if (res == 1)
-            print_usage();
-        else if (res == 2)
-            print_version();
-        exit(0);
-    }
-
-    printf("%.2Lf\n", (price * wattage) * interval);
-
-    return 0;
-}
-
-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)
-        if (argv[i][0] == '-') {
-            if (argv[i][1] == 'h' || argv[i][2] == 'h')
-                return 1;
-            else if (argv[i][1] == 'v' || argv[i][2] == 'v')
-                return 2;
-        } else if (argc < 4) {
-            return 1;
-        } else if (pos == 0) {
-            *price = price_to_wattspersecond((price_t)atof(argv[i]));
-            ++pos;
-        } else if (pos == 1) {
-            *wattage = (wattage_t)atof(argv[2]);
-            ++pos;
-        } else
-            *interval += interval_to_seconds(argv[i]);
-
-    return 0;
-}
-
-inline interval_t interval_to_seconds(const char * const interval) {
-    interval_t intrvl = (interval_t)atol(interval);
-
-    switch (interval[strlen(interval) - 1]) {
-        case 'm':
-        case 'M':
-            return intrvl * 60;
-        case 'h':
-        case 'H':
-            return intrvl * 60 * 60;
-        case 'd':
-        case 'D':
-            return intrvl * 60 * 60 * 24;
-        default:
-            return intrvl;
-    }
-}
-
-inline price_t price_to_wattspersecond(const price_t price) {
-    return price / 1000.f / 3600.f;
-}
-
-inline void print_version() {
-    puts("kwh-cost Ver. " VERSION "\n"
-         "Copyright (C) 2021,2022 Alexander \"Arav\" Andreev <me@arav.top>. All rights reserved.\n"
-         "You can see a license for this program in /usr/share/licenses/kwh-cost/LICENSE.");
-}
-
-inline void print_usage() {
-    puts("Usage: kwh-cost [OPTIONS] price wattage interval [interval ...]\n"
-         "Options:\n"
-         "  --help, -h     display this usage information.\n"
-         "  --version, -v  display program version.\n"
-         "Arguments:\n"
-         "  price     price per kWh.\n"
-         "  wattage   power usage in Watts.\n"
-         "  interval  time interval in seconds during which\n"
-         "            this much power to be constantly used.\n"
-         "            You may specify other time units such as:\n"
-         "            m'inute, h'our, d'ay. Example: 5d 3h.\n"
-         "            All given intervals will be summed up.");
-}

src/main.h

@@ -1,19 +0,0 @@
-#ifndef _MAIN_H_
-#define _MAIN_H_
-
-#define VERSION "1.1.0"
-
-typedef long double   price_t;
-typedef long double   wattage_t;
-typedef unsigned long interval_t;
-
-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(const char * const interval);
-inline price_t    price_to_wattspersecond(const price_t price);
-
-inline void print_version();
-inline void print_usage();
-
-#endif