Question

what is not there function prototype ?
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Answer 1

Explanation:

The called function is unknown because no prototype declaration exists. Calls to unknown functions risk that the number of parameters may not correspond to the actual requirements. ... Include prototypes of the functions used in your program. Prototypes must be specified before the functions are actually 

Answer 2

function prototype or function interface is a declaration of a function that specifies the function's name and type signature (arity, data types of parameters, and return type), but omits the function body.