C 运算符的优先级

Question

I am new in programming I have started learning with C. I wanted to learn about the precedence of the operators in the following

if ( p == 2 || p % 2 )

Please help me.

Answer 1

Refer Precedence Of Operators and Short Circuiting .

• Precedence: Operator precedence determines how the operators and operands are grouped within an expression when there's more than one operator and they have different precedences.

• Associativity: Operator associativity is used when two operators of the same precedence appear in an expression.

Since || exists, it is required that the left side of the ||be evaluated first to decide if the right side of ||needs to be processed. If p == 2 returns true, p % 2 will not be evaluated.

Hence p == 2 will be executed first, followed by p % 2 (because % has higher precedence than || ).

The result of these 2 will then be evaluated against ||.

Answer 2

Here

if ( p == 2 || p % 2 )

it looks like

if( operand1 || operand2)

where operand1 is p == 2 and operand2 is P % 2 . Now the logical OR || truth table is

operand1  operand2  operand1 || operand2
0         0         0
0         1         1
1         0         1
1         1         1

From the above table, it's clear that if the first operand operand1 result is true then the result will always true & second operand operand2 doesn't get evaluated .

operand1 is ==>

• p == 2 (lets assume p is 2 )

• 2 == 2 results in true hence operand2 doesn't get evaluated and if blocks looks like as

  if(true) { }

Lets assume p is 3 then operand1 ie 2 == 3 is false ie operand2 gets evaluated ie 3%2 ie 1 that means if blocks looks like

if(true)
{
}

Let's assume p is 4 then operand1 ie 2 == 4 is false ie operand2 gets evaluated ie 4%2 ie 0 that means if blocks looks like

if(false)
{
}

Hope the above explanation makes sense to you.

About the associativity and precedence, please look into manual page of operator