Thread: strings

  1. #1
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    strings

    Can anyone explain what this program is doing ! (Program is in attachment)
    Code:
    #include<stdio.h>
    int main()
    {
    	char s[]="No two viruses work similarly";
    	int i =0;
    	while(s[i]!='\0');
    	{
    		printf("%c %c\n",s[i],*(s+i));
    		printf("%c %c\n",i[s],*(i+s));
    		i++;
    	}
    	return 0;
    }
    Attached Files Attached Files
    • File Type: c A_c.c (197 Bytes, 50 views)
    Last edited by Salem; 08-29-2014 at 03:05 PM. Reason: Inline the code

  2. #2
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    You should post the code here using code tags.

  3. #3
    and the hat of int overfl Salem's Avatar
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    You might want to stare at line 6 some more, until you see a problem.
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.

  4. #4
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    Quote Originally Posted by Salem View Post
    You might want to stare at line 6 some more, until you see a problem.
    It took me almost two minutes to see it.

    Tim S.
    "...a computer is a stupid machine with the ability to do incredibly smart things, while computer programmers are smart people with the ability to do incredibly stupid things. They are,in short, a perfect match.." Bill Bryson

  5. #5
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    Quote Originally Posted by Abhishek_Kumar View Post
    Can anyone explain what this program is doing !...
    Code:
    ...
    First, yes line 6's probably should've been picked up with your compiler.
    But after fixing that, to answer your question, basically this program is showing you 4 ways an element of an array can be addressed.
    The second two ways are not recommended though.

  6. #6
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    I understand the problem on line 6, but could someone please explain to me line 9's use of
    Code:
     i[s]
    when i is defined as an int ... how is it an array or subject to array notation (i.e. the 's' as a subscript)..???

  7. #7
    C++ Witch laserlight's Avatar
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    Quote Originally Posted by trbennett
    when i is defined as an int ... how is it an array or subject to array notation (i.e. the 's' as a subscript)..?
    To understand this, refer to what the standard has to say about the definition of operator[]
    Quote Originally Posted by C99 Clause 6.5.2.1 Paragraph 2b
    The definition of the subscript operator [] is that E1[E2] is identical to (*((E1)+(E2))).
    i[s] is identical to (*((i)+(s))) which is equivalent to (*((s)+(i))) which is identical to s[i]. However, because most people would expect s[i] (and indeed the standard also states that "E1[E2] designates the E2-th element of E1 (counting from zero)", using i[s] is poor practice.
    Quote Originally Posted by Bjarne Stroustrup (2000-10-14)
    I get maybe two dozen requests for help with some sort of programming or design problem every day. Most have more sense than to send me hundreds of lines of code. If they do, I ask them to find the smallest example that exhibits the problem and send me that. Mostly, they then find the error themselves. "Finding the smallest program that demonstrates the error" is a powerful debugging tool.
    Look up a C++ Reference and learn How To Ask Questions The Smart Way

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    WOW... That is astounding.
    Thank you for the great description,
    and your description of it as "poor practice" is an understatement...

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