Array of Constants Initialization

**danlee58** · 08-29-2008

I am trying to initialize an array of Constants for an embedded computer. It's a lookup table for a non-linear function. I can't seem to get it to compile correctly. Here is the simplified Syntax:

Code:

const int junk [3][2] = {10, 2. 5, 4, 1, 6};

This is how it's used:

Code:

int trsh;
int trsh2;

trsh = 3;  //This value is input from an A/D conveter.

if (trsh == junk[0][0])
(trsh2 = junk[0][1];
else
if (trsh >= junk[1][0])
(trsh2 = junk[1][1];
else 
trsh2 = junk[2][1];

I actually extrapolate between the elements to determine the value of trsh2, but I didn't do it here for simplification.

**matsp** · 08-29-2008

Your posted code will not compile due to several syntax errors (parenthesis where I beleive you mean braces, a dot instead of comma in the intializer list for the array).

Also, a 2D array would normally have two levels of braces, e.g.

Code:

const int array[3][2] = { { 0, 1 } , { 2, 3 }, {3, 4} };

At the very least, gcc will give you a warning if you don't have the extra braces.

--
Mats

**QuantumPete** · 08-29-2008

You are also not indenting your code and your if/else statements are missing braces.

QuantumPete

**Elysia** · 08-29-2008

Code:

if (trsh == junk[0][0])
    trsh2 = junk[0][1];
else
{
    if (trsh >= junk[1][0])
        trsh2 = junk[1][1];
    else 
        trsh2 = junk[2][1];
}

This is more like how it should look like.

**kcpilot** · 08-29-2008

why the extra braces for the this:

Code:

else
{
    if (trsh >= junk[1][0])
        trsh2 = junk[1][1];
    else 
        trsh2 = junk[2][1];
}

you don't need that!

**laserlight** · 08-29-2008

why the extra braces

To improve clarity.

**kcpilot** · 08-29-2008

what clarity???

**laserlight** · 08-29-2008

The clarity of the code, of course, in addition to what the indentation provides. Put it another way: why the indentation? You don't need that!

Code:

if (trsh == junk[0][0]) trsh2 = junk[0][1];
else if (trsh >= junk[1][0]) trsh2 = junk[1][1]; else trsh2 = junk[2][1];

EDIT:
On second thought, perhaps what you mean is that we can indent like this:

Code:

if (trsh == junk[0][0])
    trsh2 = junk[0][1];
else if (trsh >= junk[1][0])
    trsh2 = junk[1][1];
else
    trsh2 = junk[2][1];

Admittedly, in answering your question, this did not cross my mind since your focus was on the braces, but we certainly could write:

Code:

if (trsh == junk[0][0])
{
    trsh2 = junk[0][1];
}
else if (trsh >= junk[1][0])
{
    trsh2 = junk[1][1];
}
else
{
    trsh2 = junk[2][1];
}

**kcpilot** · 08-29-2008

EXACTLY! And you don't need the braces there either (not even for clarity!)

**tabstop** · 08-29-2008

I'm guessing the braces are there because the actual code is bigger than one line (as hinted at by OP).

**laserlight** · 08-29-2008

Originally Posted by kcpilot

And you don't need the braces there either (not even for clarity!)

I agree, but of course it may be advised by a style guideline motivated by clarity and future proofing against misleading additions of statements, or simply for consistency.

**Elysia** · 08-29-2008

Originally Posted by kcpilot

why the extra braces for the this:

Code:

else
{
    if (trsh >= junk[1][0])
        trsh2 = junk[1][1];
    else 
        trsh2 = junk[2][1];
}

you don't need that!

Because it's more than one line.
When it is, I usually add them for more clarity.
It's purely a style question.

**vart** · 08-29-2008

I always add braces, It helps to avoid erros in the code like

Code:

if(x)
   if(y)
      statement1;
else
   statement2;

as well as prevents adding errors when the additional statements are added, or when the statement is the macro resolved to some construction like
if(p) puts(p);

**danlee58** · 08-29-2008

Thanks for the replys. The dot inplace of the comma was a typo in my example. My ANSI C book does not show two levels of braces for multi dimensional arrays. I will try that and let you know.

**whoie** · 08-29-2008

You don't need all those extra braces for the initializer though. They are entirely optional, although gcc does complain about it from what I remember. Your compiler shouldn't be bombing for that, especially since you don't have too many.

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