For 循环 in F# and C++

Introduction

The for loop is a crucial control flow statement that allows programmers to execute a block of code repeatedly. for loops have been present in programming languages for over 50 years, and they continue to be widely used in F# and C++. In this article, we will explore how for loops work in F# and C++ and provide some code examples to illustrate their usage.

F# For Loops

In F#, there are two ways to implement for loops: the for ... in ... loop and the for ... to ... do ... loop.

for ... in ... loop

The for ... in ... loop is used to iterate over a sequence of items. Here’s an example of how to use the for ... in ... loop in F#:

let names = ["Alice"; "Bob"; "Charlie"]
for name in names do
    printfn "Hello %s" name

In this example, we iterate over the sequence names and print out each name with a greeting.

for ... to ... do ... loop

The for ... to ... do ... loop is used to iterate over a range of values. Here’s an example of how to use the for ... to ... do ... loop in F#:

for i in 1 .. 10 do
    printfn "%d" i

In this example, we iterate over the range 1 .. 10 and print out each value.

C++ For Loops

In C++, there are three ways to implement for loops: the for (init; cond; inc) { ... } loop, the for (auto x : xs) { ... } loop, and the for (;;) { ... } loop.

for (init; cond; inc) { ... } loop

The for (init; cond; inc) { ... } loop is used to iterate over a range of values. Here’s an example of how to use the for (init; cond; inc) { ... } loop in C++:

for (int i = 1; i <= 10; i++) {
    std::cout << i << std::endl;
}

In this example, we iterate over the range 1 .. 10 and print out each value.

for (auto x : xs) { ... } loop

The for (auto x : xs) { ... } loop is used to iterate over a range of values stored in a container. Here’s an example of how to use the for (auto x : xs) { ... } loop in C++:

std::vector<std::string> names = {"Alice", "Bob", "Charlie"};
for (auto name : names) {
    std::cout << "Hello " << name << std::endl;
}

In this example, we iterate over the sequence names and print out each name with a greeting.

for (;;) { ... } loop

The for (;;) { ... } loop is an infinite loop that executes the code within the loop indefinitely. Here’s an example of how to use the for (;;) { ... } loop in C++:

for (;;) {
    std::cout << "Hello, world!" << std::endl;
}

In this example, we print out the greeting "Hello, world!" over and over again.

Conclusion

In this article, we covered the basics of for loops in F# and C++. We hope that you found these examples helpful and that you are now equipped to use for loops in your own programs. Remember, the for loop is a powerful tool that can help you write efficient and elegant code, so practice using it often!