Rule 13.3 - Using ++/-- with a volatile variable in C

[bsmith23]

Hello, 
I saw in a previous post (https://forum.misra.org.uk/showthread.php?tid=1302), it was discussed that 

Code:

volatile int x = 0;
x++;

where x is declared as volatile is a violation of rule 13.3 and changing this to be 

Code:

x += 1;

results in compliance with rule 13.3. Would someone be able to explain why this is the case?