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---
id: 56533eb9ac21ba0edf2244b0
title: 複合賦值之 -=
challengeType: 1
videoUrl: 'https://scrimba.com/c/c2Qv7AV'
forumTopicId: 16660
dashedName: compound-assignment-with-augmented-subtraction
---
# --description--
`+=` 操作符類似,`-=` 操作符用來對一個變量進行減法賦值操作。
```js
myVar = myVar - 5;
```
將從 `myVar` 中減去 `5`。 等價於:
```js
myVar -= 5;
```
# --instructions--
使用 `-=` 操作符對 `a``b``c` 實現相減賦值操作。
# --hints--
`a` 應該等於 `5`
```js
assert(a === 5);
```
`b` 應該等於 `-6`
```js
assert(b === -6);
```
`c` 應該等於 `2`
```js
assert(c === 2);
```
應該對每個變量使用 `-=` 操作符。
```js
assert(code.match(/-=/g).length === 3);
```
不要修改註釋上面的代碼。
```js
assert(
/let a = 11;/.test(code) && /let b = 9;/.test(code) && /let c = 3;/.test(code)
);
```
# --seed--
## --after-user-code--
```js
(function(a,b,c){ return "a = " + a + ", b = " + b + ", c = " + c; })(a,b,c);
```
## --seed-contents--
```js
let a = 11;
let b = 9;
let c = 3;
// Only change code below this line
a = a - 6;
b = b - 15;
c = c - 1;
```
# --solutions--
```js
let a = 11;
let b = 9;
let c = 3;
a -= 6;
b -= 15;
c -= 1;
```