{"id":969,"date":"2014-11-01T00:01:33","date_gmt":"2014-11-01T07:01:33","guid":{"rendered":"http:\/\/c-for-dummies.com\/blog\/?p=969"},"modified":"2014-11-08T07:49:41","modified_gmt":"2014-11-08T15:49:41","slug":"from-text-to-integer","status":"publish","type":"post","link":"https:\/\/c-for-dummies.com\/blog\/?p=969","title":{"rendered":"From Text to Integer"},"content":{"rendered":"

A program prompts for a value. The user types “12345” at the keyboard, but that input is a string and not the value 12,345. Therefore, the code must convert the string into a value. This task can be accomplished in a number of ways.
\n
\nThe easiest way to make the conversion is to use the scanf()<\/em> function:<\/p>\n

scanf(\"%d\",&value);<\/code><\/p>\n

The scanf()<\/em> function, however, won’t understand if the user screws up, potentially creating more work for you to code around that function’s peculiarities.<\/p>\n

Another option is to fetch a string and then process it through the strtol()<\/em> function. That function, defined in stdlib.h<\/code>, converts a string to a long int<\/em> variable. It allows for white space before the value, a leading +<\/code> or -<\/code> sign, and it can read in hex values prefixed by using 0x<\/code> or octal values prefixed with a leading 0<\/code> (zero).<\/p>\n

The strtol()<\/em> function<\/a> also terminates reading the string at the first non-digit character. It’s a vast improvement over the atoi(<\/em>) function, which was the C library’s original “ASCII to integer” conversion function. (The atoi()<\/em> function is also defined in stdlib.h<\/code>.)<\/p>\n

Your challenge this month is to create your own text-to-integer function. I confess that this isn’t an easy exercise. It involves reading a string — a pointer — and using ASCII text conversion tricks to translate characters into values.<\/p>\n

To assist you, I’ve created a skeleton below that provides a starting point.<\/p>\n

\r\n#include <stdio.h>\r\n\r\nint convertString(char *string);\r\n\r\nint main()\r\n{\r\n    char *value = \"24680\";\r\n    int result;\r\n\r\n    result = convertString(value);\r\n    printf(\"The string %s represents value %d.\\n\",\r\n            value,\r\n            result);\r\n\r\n    return(0);\r\n}\r\n\r\nint convertString(char *string)\r\n{\r\n}<\/pre>\n
Your tasks is to complete the code by coding the convertString()<\/em> function. You can get as fancy as you like, although the basic task is to create something that returns an int<\/em> value from the string argument. Please don’t use strtol()<\/em> or atoi()<\/em> or another C library function. That’s cheating. You need to code your own function, which can be done!<\/p>\n
As a hint, it helps to know that the ASCII codes for characters ‘0’ through ‘9’ can be converted to values 0 through 9 by subtracting 0x30 (the code for character ‘0’). So, if you were converting single characters, you could do something like:<\/p>\n
cvalue = digit - '0';<\/code><\/pre>\n
Where cvalue<\/code> is an int<\/em> variable and digit<\/code> is a single character variable holding characters ‘0’ through ‘9’ inclusive. The result of the above operation would be that cvalue<\/code> holds the integer value of character variable digit<\/code>.<\/p>\n
I will post my solution<\/a> in a week.<\/p>\n","protected":false},"excerpt":{"rendered":"
Write your own function to convert a text value to a numeric value. Continue reading →<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[3],"tags":[],"class_list":["post-969","post","type-post","status-publish","format-standard","hentry","category-exercise"],"_links":{"self":[{"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=\/wp\/v2\/posts\/969","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=969"}],"version-history":[{"count":9,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=\/wp\/v2\/posts\/969\/revisions"}],"predecessor-version":[{"id":1085,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=\/wp\/v2\/posts\/969\/revisions\/1085"}],"wp:attachment":[{"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=969"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=969"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=969"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}