省略for循环中的第一个参数

Question

In PHP, Java, C++ (and many other languages), for loops are used like this:

for(int i=0;i<10;i++)

If I already initialized i , how can I omit the initialization statement?

Answer 1

In Java, C++ and PHP it is completely valid to omit the initialization portion of the for loop

int i = 0;
...
for(; i < 10; i++);

This is true of most languages which have a for loop structure

Answer 2

for(; i < 10; i++) {
    ...
}

You can leave out any of the items in the for loop if they are not needed. You could also put in multiple things to do, or multiple conditions to check such as:

int j = 40;
for(int i = 0; i < 10 || j > 30; i++, j--) {}

Answer 3

I think for C++, PHP you could just do this. Not sure of the syntax for other languages. You could do the same with a while statement if you want to declare outside the loop.

for(;i<10;i++)

Answer 4

不要忘记，如果你有一个迭代的数组并且不想使用标准的“for”，你总是可以使用“foreach（$ array as $ var）”（在PHP上）或其他“for”（ X：）“在Java上:)