An adaptable programmable calculator is provided by employing modular read-write and read-only memory units capable of being expanded to provide the calculator with additional program and data storage functions oriented towards the environment of the user, a central processing unit, and an input-output control unit capable of bidirectionally transferring information between the memory or central processing units and a number of input and output units. The memory, central processor, and input-output control units are controlled by a microprocessor included in the central processing unit. The input and output units include a keyboard input unit with a plurality of sections capable of being defined by plug-in read-only memory modules and stored programs added by the user, a magnetic card reading and recording unit capable of bidirectionally transferring information between an external magnetic card and the calculator, a display unit capble of displaying every alphabetic and numeric character and many other symbols individually and in a line of one or more alphameric statements, and a printer unit capable of printing on thermally sensitive paper every alphabetic and numeric character and many other symbols individually and in alphameric statements or messages. The keyboard input unit includes a plurality of operand keys and a plurality of operator keys for entering algebraic statements specifying selected arithmetic operations, including relational operations, into the calculator. The operations specified in a particular algebraic statement are processed in accordance with a predetermined hierarchal priority of operations, all relational operations performed last. In the event an algebraic statement being processed specifies a plurality of operations having the same hierarchal priority, that plurality of operations is processed in the order in which they were specified during entry of that algebraic statement.