{"id":1997,"date":"2016-07-08T00:01:41","date_gmt":"2016-07-08T07:01:41","guid":{"rendered":"http:\/\/c-for-dummies.com\/blog\/?p=1997"},"modified":"2016-07-02T09:20:23","modified_gmt":"2016-07-02T16:20:23","slug":"tally-the-digits-solution","status":"publish","type":"post","link":"https:\/\/c-for-dummies.com\/blog\/?p=1997","title":{"rendered":"Tally the Digits – Solution"},"content":{"rendered":"

To solve this month’s Exercise<\/a>, you must create a function that tallies digits in an integer value, what’s known as a digit sum<\/em>. The key issue is how to peel off individual values in an integer and then total the result.
\n
\nI can think of two ways to process digits in a value, though more methods are possible.<\/p>\n

The first way is to use the modulus operator in the equation n<\/em> % 10<\/code>, where n<\/em> is any integer value. The result of that operation is the final digit in the value. So:<\/p>\n

123456789 % 10 = 9<\/code><\/p>\n

And:<\/p>\n

12345678 % 10 = 8<\/code><\/p>\n

And so on.<\/p>\n

To get from 123456789 to 12345678 you divide by 10. For a real number, you’d get:<\/p>\n

123456789 \/ 10 = 12345678.9<\/code><\/p>\n

But when working with integers, you get:<\/p>\n

123456789 \/ 10 = 12345678<\/code><\/p>\n

So my first solution for the digit_sum()<\/em> function is:<\/p>\n

\r\nint digit_sum(unsigned n)\r\n{\r\n    int total = 0;\r\n\r\n    while(n)\r\n    {\r\n        total += n % 10;\r\n        n \/= 10;\r\n    }\r\n\r\n    \/* if the value is over two-digits wide, recurse *\/<\/span>\r\n    if(total > 9)\r\n        return(digit_sum(total));\r\n\r\n    return(total);\r\n}<\/pre>\n
The while<\/em> loop peels through each digit in integer value n<\/code>. The modulus operator obtains the left-most digit, which is added to the sum in total<\/code>. Then variable n<\/code> is divided by 10 and the while<\/em> loop repeats.<\/p>\n
Once all the digits are peeled away, an if<\/em> statement tests to see whether the result is greater than 9, which means it’s more than a single-digit wide. If so, the function is recursively called in the return<\/em> statement. Otherwise, the total is returned. Click here<\/a> to view the full solution.<\/p>\n
My second solution was actually the first one I thought of: Convert the integer value into a string, then read the digits from the string, converting each one into a value. Here is the version of the digit_sum()<\/em> function:<\/p>\n
\r\nint digit_sum(unsigned n)\r\n{\r\n    char digits[32];\r\n    char *d;\r\n    int total;\r\n\r\n    \/* convert value to string *\/<\/span>\r\n    snprintf(digits,32,\"%u\",n);\r\n\r\n    \/* initialize variables *\/<\/span>\r\n    d = digits;\r\n    total = 0;\r\n\r\n    \/* tally all the individual digits *\/<\/span>\r\n    while(*d)\r\n    {\r\n            \/* subtract '0' from the character to\r\n               retrieve its value *\/<\/span>\r\n        total += *d - '0';\r\n        d++;\r\n    }\r\n\r\n    \/* if the value is over two-digits wide, recurse *\/<\/span>\r\n    if(total > 9)\r\n        return(digit_sum(total));\r\n\r\n    return(total);\r\n}<\/pre>\n
As you can see, this solution is more complex, but it still works: The snprintf()<\/em> statement converts an integer value into a string. The argument 32 ensures that the string generated fits into the digits[]<\/code> buffer without any overflow. (I’m assuming that an unsigned int<\/em> value is 32 digits wide.)<\/p>\n
Once the value is in a string, the while<\/em> loop processes each character, left-to-right. (Order doesn’t matter.) The statement total += *d - '0'<\/code> converts each digit character into a value, which is added to the total<\/code> variable. Yes, this solution involves pointers, which is scary, but you could do another version that doesn’t use pointers.<\/p>\n
As with my first solution, the value of total<\/code> is compared with 9. If it’s greater, then the digit_sum()<\/em> function is recursively called in the return<\/em> statement.<\/p>\n
Click here<\/a> to view the full solution.<\/p>\n
I’m certain that other solutions are possible, even if they’re just variations on my two solutions. As long as the digit_sum()<\/em> function returns the proper value, consider your solution good.<\/p>\n","protected":false},"excerpt":{"rendered":"
To solve this month’s Exercise, you must create a function that tallies digits in an integer value, what’s known as a digit sum. The key issue is how to peel off individual values in an integer and then total the … Continue reading →<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[5],"tags":[],"class_list":["post-1997","post","type-post","status-publish","format-standard","hentry","category-solution"],"_links":{"self":[{"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=\/wp\/v2\/posts\/1997","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=1997"}],"version-history":[{"count":4,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=\/wp\/v2\/posts\/1997\/revisions"}],"predecessor-version":[{"id":2017,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=\/wp\/v2\/posts\/1997\/revisions\/2017"}],"wp:attachment":[{"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=1997"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=1997"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=1997"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}