{"id":542,"date":"2022-08-30T15:03:05","date_gmt":"2022-08-30T15:03:05","guid":{"rendered":"https:\/\/unknownerror.org\/index.php\/2013\/11\/09\/datatypes-and-datatype-modifiers-in-c-collection-of-common-programming-errors\/"},"modified":"2022-08-30T15:03:05","modified_gmt":"2022-08-30T15:03:05","slug":"datatypes-and-datatype-modifiers-in-c-collection-of-common-programming-errors","status":"publish","type":"post","link":"https:\/\/unknownerror.org\/index.php\/2022\/08\/30\/datatypes-and-datatype-modifiers-in-c-collection-of-common-programming-errors\/","title":{"rendered":"Datatypes and datatype modifiers in C-Collection of common programming errors"},"content":{"rendered":"

I am pretty new to C. I recently came across this piece of code in C:<\/p>\n

#include \n\nint main()\n{\n        unsigned Abc = 1;\n        signed Xyz = -1;\n\n        if(AbcXyz)\n                printf(\"Great\");\n        else\n        if(Abc==Xyz)\n        printf(\"Equal\");\n        return 0;\n}\n<\/code><\/pre>\n
I tried running it and it outputs “Less”. How does it work? What is the meaning of unsigned Abc? I could understand unsigned char Abc, but simply unsigned Abc? I am pretty sure Abc is no data type! How(and Why?) does this work?<\/p>\n
    \n
  1. \n
    The default type in C is int<\/code>. Therefore unsigned<\/code> is a synonym for unsigned int<\/code>.<\/p>\n
    Singed integers are usually handled using twos complement. This means that the actual value for 1 is 0x0001 and the actual value for -1 is 0xFFFF.<\/p>\n<\/li>\n
  2. \n
    Two things are happening.<\/p>\n
      \n
    1. \n
      The default data type in C in int. Thus you have variables of type signed int and unsigned int.<\/p>\n<\/li>\n
    2. \n
      When and unsigned int and a signed int are used in an expression the signed int is converted to unsigned before the expression is evaluated. This will cause signed(-1) to turn into a very large unsigned number (due to 2’s complement representation).<\/p>\n<\/li>\n<\/ol>\n<\/li>\n
    3. \n
      As far as I know, the signed value gets promoted to an unsigned value and so becomes very large.<\/p>\n<\/li>\n
    4. \n
      int<\/code> is the “default” type in C. unsigned Abc<\/code> means unsigned int Abc<\/code> just like long L<\/code> means long int L<\/code>.<\/p>\n
      When you have an expression that mixes signed and unsigned ints, the signed ints get automatically converted to unsigned. Most systems use two’s complement to store integers, so (unsigned int)(-1)<\/code> is equal to the largest possible unsigned int<\/code>.<\/p>\n<\/li>\n
    5. \n
      Comparing signed and unsigned types result in undefined behavior<\/em>. Your program can and will print different results on different platforms.<\/strike><\/p>\n
      Please see comments.<\/p>\n<\/li>\n
    6. \n
      unsigned\/signed is just short specification for unsigned int\/signed int (source), so no, you don’t have variable with “no data type”<\/p>\n<\/li>\n
    7. \n
      The signed value will get promoted to unsigned and therefore it will be bigger than 1.<\/p>\n<\/li>\n
    8. \n
      Add the following line after signed Xyz = -1;<\/p>\n
      \nprintf(\"is Abc => %x less than Xyz => %x\\n\",Abc,Xyz);\n<\/pre>\n
      and see the result for yourself.<\/p>\n<\/li>\n<\/ol>\n
      Originally posted 2013-11-09 20:46:00. <\/small><\/p>","protected":false},"excerpt":{"rendered":"
      I am pretty new to C. I recently came across this piece of code in C: #include int main() { unsigned Abc = 1; signed Xyz = -1; if(AbcXyz) printf(“Great”); else if(Abc==Xyz) printf(“Equal”); return 0; } I tried running it and it outputs “Less”. How does it work? What is the meaning of unsigned Abc? […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[],"class_list":["post-542","post","type-post","status-publish","format-standard","hentry","category-uncategorized"],"_links":{"self":[{"href":"https:\/\/unknownerror.org\/index.php\/wp-json\/wp\/v2\/posts\/542","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/unknownerror.org\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/unknownerror.org\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/unknownerror.org\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/unknownerror.org\/index.php\/wp-json\/wp\/v2\/comments?post=542"}],"version-history":[{"count":0,"href":"https:\/\/unknownerror.org\/index.php\/wp-json\/wp\/v2\/posts\/542\/revisions"}],"wp:attachment":[{"href":"https:\/\/unknownerror.org\/index.php\/wp-json\/wp\/v2\/media?parent=542"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/unknownerror.org\/index.php\/wp-json\/wp\/v2\/categories?post=542"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/unknownerror.org\/index.php\/wp-json\/wp\/v2\/tags?post=542"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}