{"id":6755,"date":"2025-01-08T00:01:33","date_gmt":"2025-01-08T08:01:33","guid":{"rendered":"https:\/\/c-for-dummies.com\/blog\/?p=6755"},"modified":"2025-01-04T10:32:19","modified_gmt":"2025-01-04T18:32:19","slug":"emulating-the-modulus-operator-solution","status":"publish","type":"post","link":"https:\/\/c-for-dummies.com\/blog\/?p=6755","title":{"rendered":"Emulating the Modulus Operator – Solution"},"content":{"rendered":"

In an alternative universe, the C programming language lacks a modulus operator and no companion function exists in the library. What to do! Why, you code your own modulus function, which is the challenge for this month’s Exercise<\/a>.
\n
\nFor me, the weirdest part about my solution is dealing with remainders of integers. I hope you avoided the temptation to typecast values into real numbers. Yes, this operation can be performed with integers, which is good because integer division does the rounding for you.<\/p>\n

Here is my mod()<\/em> function:<\/p>\n

int mod(int x, int y)
\n{
\n    return( x-y * (x\/y) );
\n}<\/code><\/p>\n

The expression in the return<\/em> statement looks confusing — if you read it left-to-right. Because of the order of operations, the expression is evaluated from right-to-left:<\/p>\n

(x\/y)<\/code><\/p>\n

The value of x<\/code> is divided by y<\/code>, which is rounded down because these are integer values. The result is the factor of variable y<\/code> just below variable x<\/code>. So if 41 and 7 are input as x<\/code> and y<\/code>, respectively, the value returned is 5: 5×7 = 35, which is less than 41.<\/p>\n

The next step is to multiply the factor by the second value:<\/p>\n

y * (x\/y)<\/code><\/p>\n

Don’t be fooled into thinking that the computer calculates x-y<\/code> first. It does not. Instead, the value of y<\/code> is multiplied by the result of (x\/y)<\/code>, the factor just below variable x<\/code>. Again, using 41 for x<\/code> and 7 for y<\/code> you get the result 35: 7×5 or 7×(41÷7).<\/p>\n

Finally, you subtract the result of y * (x\/y)<\/code> from the original value x<\/code>:<\/p>\n

x-y * (x\/y)<\/code><\/p>\n

Using the same values as before: 41 – 7 × (41 ÷ 7). The result is the modulus of 41 and 7.<\/p>\n

Here’s the full code for my solution:<\/p>\n

2025_01-Exercise.c<\/a><\/h3>\n
\r\n\/*\r\n   Exercise January 2025\r\n   emulate the % operator\r\n*\/<\/span>\r\n#include <stdio.h>\r\n\r\nint mod(int x, int y)\r\n{\r\n    return( x-y * (x\/y) );\r\n}\r\n\r\nint main()\r\n{\r\n    int a,b;\r\n\r\n    printf(\"Enter two integers separated by a space: \");\r\n    scanf(\"%d\",&a);\r\n    scanf(\"%d\",&b);\r\n\r\n    printf(\"%% operator: %d %% %d = %d\\n\", a, b, a%b);\r\n    printf(\"mod() function: %d %% %d = %d\\n\", a, b, mod(a,b));\r\n\r\n    return 0;\r\n}\r\n<\/pre>\n
Obviously, other ways are available to solve this puzzle. I had to wiggle the expression around a few times to get the proper result, which was negative at one point in time. The final expression is short enough to be cryptic, but it works. I hope that your solution met with success.<\/p>\n","protected":false},"excerpt":{"rendered":"
In an alternative universe, the C programming language lacks a modulus operator and no companion function exists in the library. What to do! Why, you code your own modulus function, which is the challenge for this month’s Exercise.<\/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-6755","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\/6755","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=6755"}],"version-history":[{"count":5,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=\/wp\/v2\/posts\/6755\/revisions"}],"predecessor-version":[{"id":6784,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=\/wp\/v2\/posts\/6755\/revisions\/6784"}],"wp:attachment":[{"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=6755"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=6755"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=6755"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}