Update bit manipulation functions to use unsigned types for safety

- Modified setbits.c and invert.c to use ~0U instead of ~0 to prevent undefined behavior when left-shifting signed values.
- Updated comments to clarify the importance of using unsigned types for bit manipulation.
- Adjusted minscanf.c to use unsigned int for octal and hexadecimal inputs to match format specifier requirements, ensuring correct data handling across platforms.

Author: ohkimur

chapter_2/exercise_2_06/setbits.c

@@ -24,8 +24,10 @@ int main(void) {
 unsigned int setbits(int x, int p, int n, int y) {
     ++p; // First position is 0
 
-    unsigned int mask1 = (~(~(~0 << n) << p) & x);
-    unsigned int mask2 = (~(~0 << n) & y) << p;
+    // Use ~0U (unsigned) instead of ~0 (signed) to avoid undefined behavior
+    // when left-shifting. Left-shifting a negative signed value is undefined.
+    unsigned int mask1 = (~(~(~0U << n) << p) & x);
+    unsigned int mask2 = (~(~0U << n) & y) << p;
 
     return mask1 | mask2;
 }

chapter_2/exercise_2_07/invert.c

@@ -23,7 +23,9 @@ int main(void) {
 unsigned int invert(int x, int p, int n) {
     ++p; // First position is 0
 
-    unsigned int mask1 = ~(~0 << n) << p;
+    // Use ~0U (unsigned) instead of ~0 (signed) to avoid undefined behavior
+    // when left-shifting. Left-shifting a negative signed value is undefined.
+    unsigned int mask1 = ~(~0U << n) << p;
     unsigned int mask2 = ~mask1 & x;
 
     return mask2 | ~x;

chapter_7/exercise_7_04/minscanf.c

@@ -7,9 +7,10 @@ void minscanf(const char *format, ...);
 int main(void) {
     int decimal;
     int integer;
-    int octal;
-    int unsigned_decimal;
-    int hexadecimal_integer;
+    // Use unsigned int for %o and %x to match the format specifier requirements
+    unsigned int octal;
+    unsigned int unsigned_decimal;
+    unsigned int hexadecimal_integer;
     char character;
     char str[100];
     float float_point_number;
@@ -54,15 +55,18 @@ void minscanf(const char *format, ...) {
             break;
 
         case 'o':
-            scanf("%o", va_arg(arg_p, int *));
+            // %o expects unsigned int *, not int * (octal values are unsigned)
+            scanf("%o", va_arg(arg_p, unsigned int *));
             break;
 
         case 'u':
             scanf("%u", va_arg(arg_p, unsigned int *));
             break;
 
         case 'x':
-            scanf("%x", va_arg(arg_p, int *));
+            // %x expects unsigned int *, not int * (hexadecimal values are
+            // unsigned)
+            scanf("%x", va_arg(arg_p, unsigned int *));
             break;
 
         case 'c':

chapter_8/exercise_8_05/fsize.c

@@ -61,9 +61,10 @@ void fsize(char *name) {
 
     // Printed in a similary fashion to ls -l
     print_file_flags(buffer.st_mode);
-    // Using %hu (unsigned short) instead of %lu because st_nlink is nlink_t
-    // which is typically unsigned short, not unsigned long
-    printf("%hu ", buffer.st_nlink);
+    // Cast to unsigned long and use %lu for portability: nlink_t varies by
+    // platform (unsigned short on macOS, unsigned long on Linux). The cast
+    // ensures consistent formatting across platforms.
+    printf("%lu ", (unsigned long)buffer.st_nlink);
     print_file_user(buffer.st_uid);
     print_file_group(buffer.st_gid);
     print_file_size(buffer.st_size);