Console calculator, takes a string as input (like: 2+3*4-1+3) and outputs the result
Some quick observations:


Don't use using namespace std 
Prefer using \n over std::endl
Prefer prefix over postfix
You're mixing C and C++ here. Use &lt;cstring&gt;/&lt;string&gt; (depending on what you need) instead of string.h. For input have a look at the C++ I/O library
Some of your code is windows only ( system("pause") and system("cls") )
Don't define more than one variable per line
Comparing floats with ==/!= might be unsafe
There are several (probably unwanted) type conversions which you can catch by enabling warnings in your compiler of choice
Putting all the code into the main function makes this hard to read. It's better to split it up into functions
Try to avoid overly short variable names. They should always express intent to make reading the code easier.