23warning: assignment makes pointer from integer without a cast [duplicate]

Answer 1

You are missing parentheses here:

if (fp=fopen("crypt.txt","r")!=NULL)

The != operator has higher precedence than = so the compiler sees the expression like this:

if ( fp = ( fopen("crypt.txt","r") != NULL ) )

fp gets either 1 or 0 depending on whether fopen returned NULL. fp is a pointer and 0/1 is an integer, hence the warning.

You want

if ( ( fp=fopen("crypt.txt","r") ) != NULL )