if（i-2）在C语言中是什么意思？

Question

So,I understand everything in code except this if statement - if(i-2) :

for (i = -1, j = 0; i < 4; i++, j++)
    if (i - 2) 
       printf("%d\t", j * (i + 2));

Can anyone explain meaning of this if statement,does it have any influence on printf ? Thanks.

Answer 1

The statement under an if is executed if the controlling expression is true. In C, an expression that evaluates to 0 is considered false, while any other value is considered true.

So if (i-2) means the printf will get executed if i-2 is non-zero, ie when i is not equal to 2.

Answer 2

In C, an integer is treated like a boolean in an if statement:

• 0 is false
• not-zero is true

So if (i-2) is equivalent to if (i != 2) .

Answer 3

In c any value can be used in an if statement not just boolean expressions. This devolves into expression != 0. Often this is against style guides as it can be confusing and error prone.

The two following are equivalent

if (val) ...
if (val != 0) ...

So in you're case

if (i - 2)

will be true for every value of i except 2 when i-2 is 0