[quote user="Daniel Christopher"]I am trying to convert string value to float but i am getting a problem[/quote]
C function atof is part of the standard C library. I suggest that you browse Forums that deal with the C/C++ languages for information about those functions. For example, tutorialpoint has information about atof.
Computing and Numeric Precision
[quote user="Daniel Christopher"]
char* = "254.526";
I am getting a value like this, if I use the above function.
value = 254.52699999999999.
[/quote]
You need to find out about computing with binary arithmetic and how that affects decimal conversion and precision. It's a common problem and has been discussed many times in the past seven decades.