Added basic Makefile, updated README and some code fixes.

Makefile

@@ -0,0 +1,9 @@
+all:
+	$(CC) -Werror -lpam -lpam_misc -o checkpw checkpw.c
+
+clean:
+	rm -f ./checkpw
+
+install:
+	cp ./checkpw /usr/bin/
+

README.md

@@ -7,8 +7,8 @@ checkpw is a program that checks the validity of a users password on a Linux/PAM
 ```
 git clone https://git.xw3.org/hanez/checkpw.git
 cd checkpw
-gcc -lpam -lpam_misc -Werror -o checkpw checkpw.c
-sudo cp ./checkpw /usr/bin/
+make
+sudo make install
 ```
 
 # Usage:

checkpw.c

@@ -256,10 +256,10 @@ int main(int argc, char *argv[]) {
     // Authenticate the user
     if (authenticate(username, password, verbose) == 0) {
         printf("Authenticated successfully.\n");
-        exit(0);
+        return 0;
     } else {
         printf("Authentication failed.\n");
-        exit(1);
+        return 1;
     }
 }