Explanation of ++val++ and ++*p++ in C

Question

int val = 5;

printf(\"%d\",++val++); //gives compilation error : \'++\' needs l-value

int *p = &val;
printf(\"%d\",++*p++); //no error

Could

Answer 1

int j = ++val++; //gives compilation error

That because you cannot pre-increment an rvalue. ++val++ is interpreted as ++(val++) because post-increment operator has higher precedence than pre-increment operator. val++ returns an rvalue and pre-increment operator requires its operand to be an lvalue. :)

int k = ++*p++; //no error

++*p++ is interpreted as ++(*(p++)), which is perfectly valid.