ios - JSON string becomes different value when converting to float -

i'm parsing weather json local file.

 "temp_f":40.1,  "temp_c":4.5,

the problem when parse c value

nslog(@"%f", [weatherdict[@"temp_f"]floatvalue]);  //logs: 40.099998

if log string value returns 40.1.

nslog(@"%@", [weatherdict objectforkey:@"temp_f"]); //logs: 40.1

the problem seems when calling floatvalue

any ideas why happening?

you asking "why".

the complete answer found in famous article "what every computer scientist should know floating-point arithmetic": http://docs.oracle.com/cd/e19957-01/806-3568/ncg_goldberg.html

it must read unless want forever guessing why strange things happen numbers.

btw. use double, not float, unless can give me reason why float better you.

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