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preincrement v/s Post increment inside for loop

 
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preincrement v/s Post increment inside for loop
Aklesh
post 30 Aug, 2008 - 08:02 AM
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Hi all

Could you please let me know when can we use preincrement and post increment in for loop .


for (i=0;i<=4;++i);

and

for (i=0;i<=4;i++)


what is the basic difference between the two and when we use to what
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KYA
post 30 Aug, 2008 - 08:06 AM
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My understanding (and I could be wrong, it has been known to happen) is in that scenario there is no difference. i will still increment before the next iteration of the for loop.
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Martyr2
post 30 Aug, 2008 - 08:10 AM
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In this situation neither matters because that portion of the for loop is incremented at the end of an iteration. Post and pre increment really only come into play when they are actually being used in a statement which uses the value. For example...

cpp


int i = 1;

// Post increment will add 1 AFTER the cout has been executed
cout << i++ << endl;

i = 1;

// Pre increment will add 1 BEFORE cout so that cout will use the new value
cout << ++i << endl;


The first statement will show "1" since it uses the value in the print and then increments it. The second will show "2" because it increments it and then prints.

Hope that helps. smile.gif
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NickDMax
post 30 Aug, 2008 - 04:58 PM
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Well, it is generally thought that pre-increment is faster than post increment since post increment may involve a temporary variable. While there is some grain of truth to the matter it would really depend upon the compiler you were using.

So some people think that using preincrement in a for loop is more efficient:

for (i = 0; i < MAX; ++i) { ... }

Also if you want to write: i = i + 1; rather than i++ you should use ++i

This is of course assuming that the compiler creates a temporary value to store i in... since there is no NEED for it when i is not used in a larger expression -- so optimizing compilers don't waste their time.
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