为什么变量不增加？

Question

Increment operator not working.

I was learning C language expressions. I've also tried different combinations of increment operators (prefix and postfix) on the variables but the output is coming out to be same.

int i=-3, j=2 ,k=0,m;

m=++i&&++j||++k;

printf("%d%d%d%d\n",i,j,k,m);  

I expect the output to be -2311 but it comes out to be -2301 .

Answer 1

i and j are incremented because i needs to be evaluated. j also needs to be evaluated because i is non-zero.

But since this combined expression is non-zero, || short-circuits, and k++ is not evaluated or executed.

On the other hand, bitwise operators don't short-circuit. They also don't convert to booleans. If you want to evaluate all conditions and keep the same result you could write

m= (!!++i) & (!!++j) | (!!++k);

using the double negation trick to convert integer value to boolean.

Or spare another statement and simplify to (courtesy from user694733):

++i; ++j; ++k;
m = i && j || k;

Answer 2

The && and || operators short-circuit - depending on the value of the left-hand side of the expression, the right hand side may not be evaluated at all.

For the expression a || b a || b , if a is non-zero, then the result of a || b a || b is 1 regardless of the value of b , so b is not evaluated. For the expression a && b , if a is zero, then the result of a && b is zero regardless of the value of b , so b is not evaluated.

In your case, the result of ++i && ++j is non-zero, so ++k is not evaluated.