为什么在将两个正的16位整数相加后得到负整数？

I am a newbie to golang, actually, I am new to type based programming. I have only knowledge of JS.

While going through simple examples in golang tutorials. I found that adding a1 + a2 provides a negative integer value?

var a1 int16 = 127
var a2 int16 = 32767

var rr int16 = a1 + a2

fmt.Println(rr)

Result:

-32642

Excepted:

1. The compiler will throw an error as a exceeded the int16 max.
2. ( OR ) GO automatically convert the int16 to int32.
3. 32,894

Can you guys explain why it is showing -32642.

This is the result of Integer Overflow behaving as defined in the specification.

You don't see your expected results, because

1. Overflow happens at runtime, not compile time.
2. Go is statically typed.
3. 32,894 is greater than the max value representable by an int16.

It’s very simple. The 16 bit integer maps the positive part I 0 - 32767 (0x0000, 0x7FFF) and the negative part from 0x8000 (−32768) to 0xFFFF (-1).

For example 0 - 1 = -1 and it’s store as 0xFFFF.

Now in your specific case: 32767 + 127.

You overflow because 32767 is the max value for a signed 16 bit integer, but, if you force the addition 0x7FFF + 7F = 807E and convert 807E to signed 16 bit integer you obtain -32642.

You can better understand here: Signed number representations

Aditionally, check these Math Constants:

const (
    MaxInt8   = 1<<7 - 1
    MinInt8   = -1 << 7
    MaxInt16  = 1<<15 - 1
    MinInt16  = -1 << 15
    MaxInt32  = 1<<31 - 1
    MinInt32  = -1 << 31
    MaxInt64  = 1<<63 - 1
    MinInt64  = -1 << 63
    MaxUint8  = 1<<8 - 1
    MaxUint16 = 1<<16 - 1
    MaxUint32 = 1<<32 - 1
    MaxUint64 = 1<<64 - 1
)

And check the human version of these values here