三元运算符

Question

While studying CI faced something that is completely confusing my mind.

The expression is:

exp(V*log(i))?i%2?s:s--:s++;

If ternary operator is Question?Positive:Negative; I thought it was something like:

if(pow(i,V)==1&&(i%2)==0)
    s--;
 else
    s++;

However, the s does not enter in the question, should I ask what does the first expression mean?

The program worked perfectly, but I could not understand why.

The original program is:

main(){
    #define V 1

    int a, s=0, i;
    for(i=1000;i>=0;i--)
        exp(V*log(i))?i%2?s:s--:s++;
    exp(V*log(i))?printf("%d\t%d\t",-s,i):printf("%d\t%d\t", s,-i);
    getch();
}

Answer 1

如果exp（V log（i））为true，则测试是否为奇数i％2 == 1，如果返回s，甚至返回s-如果exp（V log（i））为false，返回s ++如果编写像这样比看起来容易：

exp(V*log(i))?(i%2?s:s--):s++;

Answer 2

The ternary operator tests if an expression is true. To understand this case you need to analyse it and separate the two uses of the operator:

exp(V*log(i))?i%2?s:s--:s++;

This translates to

if(exp(V*log(i))
    if(i%2)
       s;
    else
       s--;
else
    s++;

The only difference is that it is an expression and a single statement instead of the if / else version. It always returns the current value of s but changes it depending on the condition.

If exp refers to the exponential function, then unless the output is -inf the output will be !=0 so the value will evaluate to true . Note that nan will also evaluate to false and nan is the output for log when the value is outside its domain.

So basically you could translate this with a much simpler expression (unless V is zero, the value for i==0 would change):

i>0?s++:i%2?s:s--;