为什么 c++（和大多数其他语言）同时具有“for”和“while”循环？/你可以用一种类型做什么而你不能用另一种类型做什么？

Question

Why do most programming languages have two or more types of loops with almost no difference? In c++, is one of the two better for specific tasks? What about switches and if 's; is there any difference there?

If not, then an answer about why they were implemented would be appreciated.

Answer 1

There is nothing that you can do with one type that you can't do with the other, because mechanical transformations exist between them:

while (X) { body; }

can be written as

for (;X;) { body; }

and

for (A;B;C) { body; }

can be written as

{ A; while (B) { body; C; } }

The only difference is readability. The for loop puts the update-expression C at the top of the loop, making it easier to recognize certain patterns like looping through a numeric range:

for( i = 0; i < limit; ++i )

or following a linked list

for( ; ptr != nullptr; ptr = ptr->next )