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digitalmars.D.learn - preset counter variable in a for loop

reply Namal <sotis22 mail.ru> writes:
Hello,

I don't understand why this simple code causes a compiler error..

import std.stdio;

void main(){

  int b = 0;

  for (b; b<3; b++){
    writeln(b);		
  }
}

$Error: b has no effect

Same works perfectly fine in C++

#include <iostream>

int main(){
  int i = 0;

  for(i; i<3; i++)
    std::cout<<i<<'\n';
}

Please help me find what I am doing wrong. Thx
Feb 28 2020
parent reply mipri <mipri minimaltype.com> writes:
On Friday, 28 February 2020 at 12:44:52 UTC, Namal wrote:

 Hello,

 I don't understand why this simple code causes a compiler 
 error..

 import std.stdio;

 void main(){

  int b = 0;

  for (b; b<3; b++){
    writeln(b);		
  }
 }

 $Error: b has no effect


Well, that's the error. b has no effect, so there's
no need for it, and it's likely written in error. It
has no effect in C++ either, and you may get a warning:

example.cc: In function 'int main()':
example.cc:7:8: warning: statement has no effect [-Wunused-value]
   for (b; b<3; b++){
Feb 28 2020
parent Namal <sotis22 mail.ru> writes:
On Friday, 28 February 2020 at 12:48:17 UTC, mipri wrote:

 On Friday, 28 February 2020 at 12:44:52 UTC, Namal wrote:

 Hello,

 I don't understand why this simple code causes a compiler 
 error..

 import std.stdio;

 void main(){

  int b = 0;

  for (b; b<3; b++){
    writeln(b);		
  }
 }

 $Error: b has no effect


 Well, that's the error. b has no effect, so there's
 no need for it, and it's likely written in error. It
 has no effect in C++ either, and you may get a warning:

 example.cc: In function 'int main()':
 example.cc:7:8: warning: statement has no effect 
 [-Wunused-value]
   for (b; b<3; b++){


Thanks, I didn't know that you don't need it there and can leave 
it out!
Feb 28 2020