Misc #13230: Better Do ... while structure

• Status: Rejected
• Assignee: -

[jzakiya (Jabari Zakiya)]

I just saw this, and thought I'd pass it along.

http://ncomputers.org/suggestions/do%20while.cpp

Do ... while structure improvement
Sometimes the use of jumps such as: continue, break, goto, call to a function, etc. is necessary to avoid the execution of some instructions.

This is the case of the seed, warp and swap loops of this solution for the n queens problem.

To avoid the use of jumps or tricks like for(;;) if(condition)break; on some of these cases, we are suggesting the below improvement to the do ... while loop str


/* author: ncomputers.org */
int main(){
    // Allow initializers (extra improvement)
    do(bool condition=0){
        // Block A
    }while(condition){
        // Block B
        // Variables declared inside the initializer still visible
    }
    return 0;
}

[shyouhei (Shyouhei Urabe)]

• Status changed from Open to Feedback

I'm sorry but I have to say I don't understand how the construct works. Looking at the original site there is an example:

/* author: ncomputers.org */
#include<iostream>
using namespace std;

int main(){
    unsigned a[]={0,1,2,3,4,5,6,7,8,9};
    do(unsigned b=0){
        cout<<a[b];
    }while(++b<10){
        cout<<',';
    }
    cout<<endl;
    return 0;
}

1. At sight, I have no idea what this code does, nor how it works.
2. By closely looking at the description in http://ncomputers.org/examples/do%20while%201.cpp , it says "prints the content of an array, separating each of its elements by a comma". Now I'm totally puzzled. I don't understand why that is possible by the code, especially how the variable b changes over time.

Maybe I'm just a hard-headed nuts.

[nobu (Nobuyoshi Nakada)]

Probably it equals:

    unsigned b=0;
    do {
        cout<<a[b];
        if (!(++b<10)) break;
        cout<<',';
    } while (1);

or

    for (unsigned b=0; cout<<a[b], (++b<10);) {
        cout<<',';
    }

If it were in Ruby:

b = 0
while true
  STDOUT << a[b]
  break unless (b += 1) < 10
  STDOUT << ','
end

b = 0
while (STDOUT << a[b]; (b += 1) < 10)
  STDOUT << ','
end

b = 0
while begin
    STDOUT << a[b]
    (b += 1) < 10
  end
  STDOUT << ','
end

[matz (Yukihiro Matsumoto)]

• Status changed from Feedback to Rejected

You haven't explained the reason behind the proposal. We don't understand why you think it's "better".
If you think you can persuade us with real-world use-case, try to reopen the issue.

Matz.