我想問幾時個if 擺前幾時擺中間

We only use IF at the beginning :

IF I can't meet the bus at 7:30 a.m., I will be late.

IF I won the prize, I would give it to my Mum.
如果你想擺 if 中間 就用whether
Whether 有"其一"的意思如:

we should go home whether by bus or train.

即是不是搭"公共汽車"便是答"公共汽車"回家, 二取之其一

whether當然可以有第二種使用方式

i don't know whether she is coming

但這句表示了"她來"及 "她不來"的結果, 她只會來或不來, 也是二中其一

如果個main clause響前面,,
if就會響中間..
就好似咁樣:you will be fat if you eat so much.
you will be fat ---main clause
如果main clause響後面..
if就會響前面..
e.g.if you eat so much, you will be fat.
you will be fat---main clause

其實If何時擺在前面以及擺在中間，是有特別的規定的，其關鍵在於小小的標點——逗號，我列舉一些例子給給看看先：

If 擺在前面：（次例子中，句子被分成了2個分句，中間用逗號分割）
If it rains,we will not go on a field tomorrow.
If Jackson does well in his study,his father will be very happy.


If擺在中間：：（次例子中，句子中只有1句，中間沒有用逗號分割）
We will not go on a field if it rains tomorrow.
Jackson's father will be very happy if he does well in his study.

這些都是非常簡單的例子而已，不要見笑。希望能助你一臂之力！

If you are a good girl, I will bake you a cake.
I will bake you a cake if you are a good girl.


如果個if 0係前面, 就一定要有 (，) 0係中間
如果個if 0係中間, 就冇(，)
只係因果擺法唔同~~

記住，if 係假設的
一定要用 will / may etc 0既verb,
而唔可以用past tense / past continuous tense etc.

其實無特定, 視乎你想將句子入面邊個做 subject .