Thread: error: expected declaration specifiers or '...' before numeric constant

This is a declaration of a function named ptostruct that takes an int argument and has a return type of void:

Code:

void ptostruct(int );

This is a syntax error since 5 is not a type name:

Code:

void ptostruct(5);

You probably wanted to call the function:

Code:

ptostruct(5);

By the way, there is no need to leave out the parameter name in the declaration. Just write:

Code:

void ptostruct(int i);

This can even be pretty convenient when you copy and paste from the function definition.

Also, why place the function declaration in the main function body? It is more typical to place it at file scope, like the function definition.