code teaser

[Gurm]

Belwarrior:

If you look up, that was my first solution.

- Gurm

[Gurm]

Now the REAL question - which is faster on today's architectures:

i < n

or

i + n

Answer at 11.

- Gurm

[Umfriend]

Never done any c, but what about

int i, n = -20;
for (i = 0; i < n; i--)
printf("-");

I never did C nor C++, but if you use the first solution by Gurm, don't you run into the problem that "n" is not declared as a variable?

[Ribbit]

Originally posted by cjolley
if i=40 and n=20 how does i&lt;n run even once?

D'oh! I was so not with it.

[Wombat]

Nope. The way C declarations work, a comma-separated list of variable names can be called between the type (int) and the semi-colon.

[Gurm]

Umf,

Again, the loop will never run even once, since i will NEVER be less than n at the start.

- Gurm

[Ribbit]

Originally posted by Gurm
Now the REAL question - which is faster on today's architectures:

i < n

or

i + n

Answer at 11.

GCC produces less code for 'i+n', so that's what I'll go with.

[Wombat]

All depends on who does the coding. I don't trust a compiler to give me "fastest."

[cjolley]

I think he's talking about clock cycles.
You need to look up the op codes for the processor and find out how long cmp takes compared to add and etc.
It may also depend on whether the machine compile puts the values in registers or not before doing the operations.
chuck

[Rob(QG)]

For i+n to be faster it also relies on the Zero Flag being set by the addition operator (not sure with x86, believe Z80 didn't set it) - otherwise you would code something like this at best:

ADD AX,BX
AND AX,AX
JZ endif

or this at worst:

ADD AX,BX
CMP 0
JZ endif

[Umfriend]

ahh, so its is a "while", not a "until"? Thx, just learned my first bit of C...

[Gurm]

Umf,

It's neither. It's a FOR, not a WHILE. There is no "until".

There's for, while, and do... while.

- Gurm

[Wombat]

Originally posted by Gurm
Umf,

It's neither. It's a FOR, not a WHILE. There is no "until".

There's for, while, and do... while.

- Gurm

I hear what Umf is trying to say. Yes Umf, it's more like a "while" than like an "until." In C, a "for" loop is tested at the beginning of each execution, and may not even execute once if the condition is never true. A "do{}while" is always executed at least once, and is tested at the end of execution to see if it's going to run again.

[cjolley]

Originally posted by Gurm
Umf,

It's neither. It's a FOR, not a WHILE. There is no "until".

There's for, while, and do... while.

- Gurm

The word may be "for", but c "for" loops are realy "while" constructs.
The increment is optional and there is not even an implied "next".
By that I mean that, while it is common to use x++ or -- (or ++x, --x if you realy want to get confused while debuging), they are not part of the for syntax of "for"at all.
In fact, unless I'm not remembering correctly*,
for(i=x; i&lt;j;--i)
would decrement i even if j&lt;i , at least on old compilers

chuck

*Like that never happens.

[Umfriend]

I tried c once, after typing the program hello.c I simply stopped. Still glad I did.....
Thx all