Thread: Can anyone explain what this section code is doing ?

It would be hard to describe much here on a macro level because we don't know what all these variables are for. But I can provide a quick point about some basic syntax:

Code:

if(ge_event_ready)

Is a truth test. "Truth" in C (and most programming languages I'm aware of) indicates a value that is non-zero. "Falsity" indicates a zero value. A NULL pointer in C is considered a zero value.

Beyond that you may want to try some more specific questions.

Step 1 is don't omit the optional braces.

Code:

	for(j=1;j<=111;j++) {
		reorder_ge_event[j]=0;
	}

It takes a fraction of a second to add them when you're editing the code (some editors will automatically add } for each { you insert).

Finding them when they're missing (and shouldn't be) can take days in a lot of code.


Next, modularise!

Code:

void showDebug( const char *msg, int len, int *event, int *energy ) {
	int	i;
	printf("%s=%d\n", msg, len );
	for(i=1;i<=len;i++)
	{
		printf("\tid:%d \tenergy:%d\n",event[i],energy[i]);
	}
}

void clearArray ( int len, int *array ) {
	int	i;
	for(i=1;i<=len;i++)
	{
		array[i] = 0;
	}
}


if(ge_event_ready)
{
	const int maxlen = 111;
	if(ndo[1]==0) {
		showDebug( "BEFORE REORDERING", ge_event_fold, ge_event_id, ge_event_energy );
	}

	clearArray( maxlen, reorder_ge_event );

	for(i=1;i<=ge_event_fold;i++)
	{
		reorder_ge_event[ge_event_id[i]]=ge_event_energy[i];
	}

	k=0;
	for(i=1;i<=maxlen;i++)
	{
		if(reorder_ge_event[i]!=0)
		{
			k++;
			ge_event_id[k]=i;
			ge_event_energy[k]=reorder_ge_event[i];
		}			  
	}

	clearArray( maxlen, reorder_ge_event );

	if(ndo[1]==0) {
		showDebug( "AFTER REORDERING", ge_event_fold, ge_event_id, ge_event_energy );
	}
}

When you find yourself repeating basically the same code - say by copy/paste and change a few things, then create a function to do the work.

Then you're not staring at so much detail all at once.

Without knowing the context of the code snippet ("we don't know what all these variables are for"), describing to you what the code does is pretty boring: any novice in C should be able to figure out what the code does, line by line, because it consists of routine constructs used in routine ways.

Where did you find this code snippet? Why do you want to know what it does?

Oh, my mistake. One way to see how this might work is to consider an example. Consider:
Let ge_event_fold = 2.
Let ge_event_id[1] = 3.
Let ge_event_id[2] = 1.
Let ge_event_energy[1] = 123.
Let ge_event_energy[2] = 456.

At first all elements of reorder_ge_event are reset to 0. Then:
reorder_ge_event[ge_event_id[1]] = ge_event_energy[1];
hence:
reorder_ge_event[3] = 123;
likewise:
reorder_ge_event[1] = 456;

Next, the elements of reorder_ge_event are traversed from 1 to 111. Only those with non-zero values are processsed. Therefore,
ge_event_id[1] = 1;
ge_event_energy[1] = reorder_ge_event[1] = 456;
and:
ge_event_id[2] = 3;
ge_event_energy[2] = reorder_ge_event[3] = 123;

Observe that ge_event_id is now sorted in ascending order, and ge_event_energy is sorted correspondingly. How this works is that reorder_ge_event is a map of the crystal number and corresponding energy. By iterating over it in order of crystal number, one can then reorder the corresponding energy according to crystal number, instead of the original event number.