Interpretation of an integer division - C code

Question

I have the following C code:

int count = 0; // relative time
int T1 = 20; // period 1 in ms
int T2 = 50; // period 2 in ms
int T3 = 80; // period 3 in ms
   while (1) {
      if (count%T1 == 0) function1();
      if (count%T2 == 0) function2();
      if (count%T3 == 0) function3();
      count++;
      if (count == T1*T2*T3) count = 0;
      delay(1); // wait for 1 ms
   }

I'd like to know the reason for which there is the integer division count%T1==0 instead of count==T1. Maybe it takes into account the fact that the period T1 may not be an integer?

Thank you in advance.

Matteo Pacini · Accepted Answer · 2020-02-08 09:29:26Z

6

From the code you posted, it looks like that:

function1 will be called every 20ms
function2 will be called every 50ms
function3 will be called every 80ms
The counter resets at 80 seconds (20*50*80ms).

The keyword here is every.

Let's take function1 trigger as example.

If you write count == T1, function1 will only get executed once before a reset, when count is equal to 20.

If you want to run function1 every 20ms, you would expect it to execute at 20ms, 40ms, 60ms, and so on.

To translate this concept into code, you check if the counter is divisible by 20 via the modulo operator, hence the count % T1 expression.

Same concept applies to T2 and T3 checks.

answered Feb 8, 2020 at 9:29

Matteo Pacini

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1 Comment

Gennaro Arguzzi Over a year ago

Hi @MatteoPasini can I use the condition count==T1 if I replace count=T1*T2*T3 with count=max(T1, T2, T3)?

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