Broken Calculator

My Code : https://ide.codingblocks.com/s/171109

I am not able to find out , what i am doing wrong here . Only 1 testcase is passing.

@rk_city hey ravi your code is very complex so please tell me your approach first so that we can discuss it all.

As I am coding in C++, so I have to implement big int in C++.
I am storing numbers in string and doing operations on string only . (Operations like multiplying,adding and subtracting)

@Yashwardhan_Gautam bhaiya can you please tell me something on this topic

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