Ask a simple question about the linuxshell Program

Ask a simple linuxshell Program-Linux general technology-Linux programming and kernel information. The following is a detailed description. Example of the interrupt loop command:
#! /Bin/bash
I = 0
While [$ I-lt 10]
Do
I = 'expr $ I + 1'
If [$ I-eq 3]
Then continue
Fi
If [$ I-eq 7]
Then break
Fi
Echo "$ I"
Done

Error after running: syntax error near unexpected token 'then'
Why is this ......

Another question
#! /Bin/bash
Num = 0
While [$ num-lt 10]
Do
Echo-n "$ num"
Num = 'expr $ num + 1'
Done
Echo
Echo Loop exit.
No number is displayed after running. test:-lt: unary operator expected
This is why,