if语句

一个简单的if语句例子：

Go

package main

import "fmt"

func returnValues(ok bool) (int, bool) {
	return 5, ok
}

func main() {
	a := 5
	b := 5
	if a == b {
		fmt.Print("a is equal to b\n")
	} else {
		fmt.Print("a is not equal to b\n")
	}

	if n, ok := returnValues(true); ok {
		fmt.Printf("ok is true, n: %d\n", n)
	} else {
		fmt.Printf("ok is false, n: %d\n", n)
	}
}

Output

a is equal to b
ok is true, n: 5

Program exited.

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在if语句中声明的变量作用域仅为if语句内部。下面的例子会编译失败：

Go

package main

import "fmt"

func returnValues(ok bool) (int, bool) {
	return 5, ok
}

func main() {
	if n, ok := returnValues(true); ok {
		fmt.Print("ok is true, n: %d\n", n)
	} else {
		fmt.Print("ok is false, n: %d\n", n)
	}

	// n只在if语句内可见，所以这会在编译时报错
	fmt.Printf("n: %d\n", n)
}

Output

./prog.go:17:24: undefined: n

Go build failed.

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