From 8b718555012492253951b63eb33b45e22a2ce807 Mon Sep 17 00:00:00 2001 From: zlg Date: Sat, 2 Mar 2013 08:23:14 -0600 Subject: Solve Exercise 2-3: Hex to integer converter This exercise was fun, and I learned a simpler way to convert them. --- ch2/2-03_hex-to-int.c | 48 ++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 48 insertions(+) create mode 100644 ch2/2-03_hex-to-int.c (limited to 'ch2') diff --git a/ch2/2-03_hex-to-int.c b/ch2/2-03_hex-to-int.c new file mode 100644 index 0000000..566bd75 --- /dev/null +++ b/ch2/2-03_hex-to-int.c @@ -0,0 +1,48 @@ +#include +#include + +/* The C Programming Language, 2nd Edition + * + * Exercise 2-3: Write the function htoi(s), which converts a string of + * hexadecimal digits (including an optional 0x or 0X) into its equivalent + * integer value. The allowable digits are 0 through 9, a through f, and A + * through F. + * + * Answer: ctype.h has some cool functions in it. Using just two functions from + * that header, my function's length is much shorter than it would be if I + * were to wing it alone with C primitives. + * + * Anyway, the idea is to make sure you're working with a hex digit, + * homogenize the case of the letters, and ignore x's. Since hex is base-16 + * instead of base-10, plug a 16 in and perform some clever math based on + * ASCII knowledge. + * + * Since the function can be objectively proven correct, I included test cases + * to ensure that its output is correct. + * + * `man ascii` for more info, if you're using an OS that's actually useful. + */ + +int htoi(char s[]) { + int i, val; + + for (i = val = 0; isxdigit(s[i]) || toupper(s[i]) == 'X'; ++i) { + if (toupper(s[i]) == 'X') { + continue; + } + if (s[i] > '9') { + val = 16 * val + (toupper(s[i]) - '7'); + // The 7 is because 'A' is 7 higher than '9' in ASCII and thus only needs + // to be knocked down by that much to fall in line with the normal integer + // conversion + } else { + val = 16 * val + (s[i] - '0'); + } + } + return val; +} + +int main() { + printf(" HEX | DECIMAL\n---------------\n 1 = %3d\n 0xf = %3d\n0X64 = %3d\n fF = %3d\n 093 = %3d\n", htoi("1"), htoi("0xf"), htoi("0X64"), htoi("fF"), htoi("093")); + return 0; +} -- cgit v1.2.3-54-g00ecf href='/vgstash/log/?h=next&id=e7bccb17a6dfffd71349ab265906740562047101&follow=1'>root/tests/data (unfollow)
AgeCommit message (Expand)AuthorFilesLines
2018-10-18vgstash.DB.__init__: fix error output formattingzlg1-1/+1
2018-10-18README: fix inline <code> formattingzlg1-3/+4
2018-10-18cli: show msg if game to be deleted is not in DBzlg2-2/+12
2018-10-18README: expand on usage, cover shell quotingzlg1-7/+99
2018-10-18cli: Tell the user when a game lacks noteszlg2-3/+15
2018-10-18Catch when an invalid list filter is passedzlg4-3/+24
2018-10-12cli: Add zero-game import/export messageszlg2-11/+18
2018-10-10Bump to 0.3beta1 for PyPIzlg1-1/+1
2018-10-10Move tests and data to dedicated directoryzlg7-10/+26
2018-10-10cli: Add "export" commandzlg2-5/+54
2018-10-10cli: Add "import" commandzlg5-1/+76
2018-10-09Bump to 0.3alpha6 for PyPIzlg1-1/+1
2018-10-09cli: Add "notes" commandzlg2-4/+74
2018-10-09update_game: ensure notes are also savedzlg1-2/+2
2018-10-09cli: add 'update' commandzlg3-20/+92
2018-10-06cli: Add "delete" commandzlg2-0/+19
2018-10-06Remove ID field from DBzlg3-38/+46
2018-10-06cli: change "Status" heading to "Progress"zlg2-36/+40
2018-09-29Bump to 0.3alpha5 for PyPIzlg1-1/+1
2018-09-29cli: Add pretty printing to 'list' commandzlg3-17/+107
2018-09-08setup.py: Bump to alpha4 for PyPIzlg1-1/+1
2018-09-08cli: add '--raw' option to list commandzlg2-9/+45
2018-09-08Add remaining filters to vgstash packagezlg1-2/+11
2018-09-04Update LICENSE to match setup.pyzlg1-80/+67
2018-09-03Branch off from master with pytest, tox, clickzlg16-778/+779
2018-03-18Flesh out filter types and ownership statuszlg3-82/+144
2018-03-18README.mdown: break line correctlyzlg1-1/+1
2018-03-18add 'playlog' list filterzlg2-2/+9
2018-03-13Update helpers a bitzlg1-2/+9
2018-03-13Make VGSTASH_DB_LOCATION point to a filezlg2-21/+20
2016-11-18Remove settings from helpers.shZe Libertine Gamer1-5/+0
2016-11-15Correct phrasing in README.Ze Libertine Gamer1-4/+4
2016-11-13DerpZe Libertine Gamer1-0/+1
2016-11-03Improve error handling in shell scriptsZe Libertine Gamer4-3/+23
2016-10-24Correct run_again, add recursionZe Libertine Gamer1-0/+4
2016-10-21Add quotes to correct behavior for arglistZe Libertine Gamer1-1/+1
2016-10-14updater.sh: add recursion, error handlingZe Libertine Gamer1-43/+101
2016-10-14Correct pipe-handling behaviorZe Libertine Gamer1-1/+9
2016-10-12Clarify a method to move between platformsZe Libertine Gamer1-2/+5