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[TechnicalTalk]

 TechnicalTalk » Programming and Web Development » C/C++
 Pre and Post increment operators in C++ or Java

[researchpro]

researchpro  

 Pre and Post increment operators in C++ or Java

int a=10;
cout<< ++a; // Pre increment      a becomes 11 after this statement   prints 11
cout<< a++, // Post increment     a becomes 12 after this statement   prints 11
There is many times a confusion between these two operators. So, let it be clear. Preincrement operator increment value by one and displays the incremented result(on cout ++a).  Postincrement operator increment value by one and displays the non-incremented result(on cout a++).

[polas]

polas  

 Re: Pre and Post increment operators in C++ or Java

You are missing the bigger picture - it is a question of precidence.

Pre ++a (certainly in C, I assume the same in Java) has (amongst) the highest precidence, Post a++ has amonst the lowest precidence.

So, more generally,

int a=2;
int b=10;
int c = a + b++;
c=a + ++b;

The two values of c will be different

[TrueDestroyer]

TrueDestroyer  

 Re: Pre and Post increment operators in C++ or Java

What's more fun is putting this stuff into a chain and trying to figure out what it means.

#include<cstdio>

int main(){
  int a = 1, b = 2, c = 1, d = 0;
  (a+d-c)?a++:--a = (--a)?(c--)?--d:a++:b--;
  printf("%d\n",a);
}

At least I think that will compile...

[polas]

polas  

 Re: Pre and Post increment operators in C++ or Java

lol, its not fun when they are asking at a job interview what the value of a certain variable is though!

[TrueDestroyer]

TrueDestroyer  

 Re: Pre and Post increment operators in C++ or Java

We have different definitions of fun then. =P

I have a teacher that can absolutely flabbergast an entire class with obfuscation. Of course, he also is the original author of the Jargon file, so what would you expect?

[polas]

polas  

 Re: Pre and Post increment operators in C++ or Java

lol, I assume you have seen this well known piece of C before?

Code:

#include <stdio.h>
main(t,_,a)char *a;{return!0<t?t<3?main(-79,-13,a+main(-87,1-_,
main(-86,0,a+1)+a)):1,t<_?main(t+1,_,a):3,main(-94,-27+t,a)&&t==2?_<13?
main(2,_+1,"%s %d %d\n"):9:16:t<0?t<-72?main(_,t,
"@n'+,#'/*{}w+/w#cdnr/+,{}r/*de}+,/*{*+,/w{%+,/w#q#n+,/#{l,+,/n{n+,/+#n+,/#\
;#q#n+,/+k#;*+,/'r :'d*'3,}{w+K w'K:'+}e#';dq#'l \
q#'+d'K#!/+k#;q#'r}eKK#}w'r}eKK{nl]'/#;#q#n'){)#}w'){){nl]'/+#n';d}rw' i;# \
){nl]!/n{n#'; r{#w'r nc{nl]'/#{l,+'K {rw' iK{;[{nl]'/w#q#n'wk nw' \
iwk{KK{nl]!/w{%'l##w#' i; :{nl]'/*{q#'ld;r'}{nlwb!/*de}'c \
;;{nl'-{}rw]'/+,}##'*}#nc,',#nw]'/+kd'+e}+;#'rdq#w! nr'/ ') }+}{rl#'{n' ')# \
}'+}##(!!/")
:t<-50?_==*a?putchar(31[a]):main(-65,_,a+1):main((*a=='/')+t,_,a+1)
  :0<t?main(2,2,"%s"):*a=='/'||main(0,main(-61,*a,
"!ek;dc i@bK'(q)-[w]*%n+r3#l,{}:\nuwloca-O;m .vpbks,fxntdCeghiry"),a+1);}

[TrueDestroyer]

TrueDestroyer  

 Re: Pre and Post increment operators in C++ or Java

Oh yeah, I love that song.

[polas]

polas  

 Re: Pre and Post increment operators in C++ or Java

Oh yeah, I love that song.

 

[juanharris1]

juanharris1  

 Re: Pre and Post increment operators in C++ or Java

I have a teacher that can perfectly bowl over an entire class with obfuscation.  Of course, he also is the original author of the Jargon file.

[sidharthbanyal]

sidharthbanyal  

 Re: Pre and Post increment operators in C++ or Java

Pre increment means incrementing value the using it. Post incrementing means using value first then increasing it

[mak14317]

mak14317  

 Re: Pre and Post increment operators in C++ or Java

int a=5,i;

i=++a + ++a + a++;
i=a++ + ++a + ++a;

    a=++a + ++a + a++;
 answer is 20 in both cases...........

[johnpitter]

johnpitter  

 Re: Pre and Post increment operators in C++ or Java

Post Increment means the value is returned before the increment is made. Pre Increments means the value is returned after the increment is made,

[john14317]

john14317  

 Re: Pre and Post increment operators in C++ or Java

The pre-increment was specifically designed for "C" on the DEC PDP-11 (remember "C" has only fundamental types), because there was a specific hardware instruction that performed this operation directly on the mrmory location, without the overhead of a load,add,store sequence. The result was significantly faster.

There are still a few processors that can do this more efficiently (than the post increment of a fundamental type), but processors are often 1000's of times faster today and the situations are extremely rare. The only place I can (possibly) recomment the use of a post increment is:

[the_purple_ink]

the_purple_ink  

 Re: Pre and Post increment operators in C++ or Java

surely, everyone gets confused with the increments stuff here.. lol..