{"id":4958,"date":"2021-09-08T00:01:08","date_gmt":"2021-09-08T07:01:08","guid":{"rendered":"https:\/\/c-for-dummies.com\/blog\/?p=4958"},"modified":"2021-09-04T09:52:06","modified_gmt":"2021-09-04T16:52:06","slug":"scramble-a-string-solution","status":"publish","type":"post","link":"https:\/\/c-for-dummies.com\/blog\/?p=4958","title":{"rendered":"Scramble a String – Solution"},"content":{"rendered":"

For this month’s Exercise<\/a>, my solution to the scramble()<\/em> function requires a second array. You could code a scramble()<\/em> function without using a second array (or storage buffer), swapping individual characters within the string, but I chose not to.
\n
\nThe scramble()<\/em> function’s first task is to create a char<\/em> buffer large enough to store the incoming string. Further, I want the buffer to be filled with the null character, \\0<\/code>. The calloc()<\/em> function handles this task, using variable key<\/code> as the char<\/em> pointer to hold the allocated buffer’s address and len<\/code> as the string size, plus one for the terminating null character:<\/p>\n

key = calloc( len+1, sizeof(char) );<\/code><\/p>\n

Upon success, my solution uses the key<\/code> buffer to store the scrambled string. Here is my complete scramble()<\/em> function:<\/p>\n

\r\nvoid scramble(char *p,int len)\r\n{\r\n    char *key;\r\n    int x,r;\r\n\r\n    \/* allocate the temporary string and\r\n       fill will null characters *\/<\/span>\r\n    key = calloc( len+1, sizeof(char) );\r\n    if( key==NULL )\r\n    {\r\n        fprintf(stderr,\"Memory allocation error\\n\");\r\n        exit(1);\r\n    }\r\n\r\n    \/* process the string *\/<\/span>\r\n    x = 0;\r\n    while(x<len)\r\n    {\r\n        r = rand() % len;        \/* generate random value *\/<\/span>\r\n        if( !*(key+r) )          \/* look for a null char *\/<\/span>\r\n        {\r\n            *(key+r) = *(p+x);   \/* assign the character *\/<\/span>\r\n            x++;                 \/* increment the offset *\/<\/span>\r\n        }\r\n    }\r\n\r\n    \/* update the scrambled string *\/<\/span>\r\n    strcpy( p, key);\r\n}<\/pre>\n
Variable x<\/code> acts as an index into the passed string p<\/code>. The while<\/em> loop spins until all characters in p<\/code> are processed.<\/p>\n
First, a random value r<\/code> is generated between 0 and the string’s length, len<\/code>.<\/p>\n
Next, a test is done to determine whether a null character exists at position r<\/code> in buffer key<\/code>: if( !*(key+r) )<\/code> This expression is true when the character is null. Otherwise, the while<\/em> loop keeps spinning with additional random values generated.<\/p>\n
When a null character is found in key<\/code>, it’s replaced by the sequential character in p<\/code>, referenced by variable x<\/code>:<\/p>\n
*(key+r) = *(p+x);<\/code><\/p>\n
Variable x<\/code> is then incremented, and the while<\/em> loop continues.<\/p>\n
Click here<\/a> to view my full solution, which includes the header files stdio.h<\/code>, stdlib.h<\/code>, string.h<\/code>, and time.h<\/code>. Each of these are required for functions used in the main()<\/em> skeleton presented in the original post, so none of them should surprise you.<\/p>\n
This solution reminds me of the Lotto code in my C programming books. It works on a similar basis: using an array to track random items. Though the “array” in my scramble()<\/em> function is an allocated buffer, the concept is the same.<\/p>\n
I hope your solution meets with success. Especially if you used the character swap method, which I would find a fascinating approach to the problem.<\/p>\n","protected":false},"excerpt":{"rendered":"
For this month’s Exercise, my solution to the scramble() function requires a second array. You could code a scramble() function without using a second array (or storage buffer), swapping individual characters within the string, but I chose not to.<\/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-4958","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\/4958","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=4958"}],"version-history":[{"count":5,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=\/wp\/v2\/posts\/4958\/revisions"}],"predecessor-version":[{"id":4973,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=\/wp\/v2\/posts\/4958\/revisions\/4973"}],"wp:attachment":[{"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=4958"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=4958"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=4958"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}