AP Computer Science Principles Exam

• The 2020 AP Computer Science Principles Exam is 2 hours long with 74 multiple-choice questions.
• Programming reference materials are provided.
• The exam uses two programming formats, text-based and block-based.
• Programming instructions use numbers, Booleans, strings, and lists data types.
• Exam instructions might include assignment, display, and input, arithmetic operators, relational operators, selection, iteration, list operations, procedures and robots.

Assignment

• The instruction a ← expression evaluates the expression and assigns the result to variable a.

Display

• The instruction DISPLAY (expression) displays the value of the expression, followed by a space.

Input

• The instruction INPUT () accepts a value from the user and returns it.

Arithmetic Operations

• +, -, *, and / are used to perform arithmetic on a and b.
• 3 / 2 evaluates to 1.5.

Modulo Operator

• The modulo operator gets the remainder when a is divided by b.
• Assumes that a and b are positive integers.
• 17 MOD 5 evaluates to 2.

Random Numbers

• RANDOM (a, b) can be used to generate random integers
• Evaluates to a random integer from a to b, including a and b.
• RANDOM (1, 3) could yields 1, 2, or 3.

Relational and Boolean Operators

• Comparison operators =, ≠, >, <, , and  evaluate the relationship between two variables, expressions, or values.
• a = b evaluates to true if a and b are equal; otherwise it evaluates to false.

NOT operator

• NOT condition will evaluate to true if the condition is false, and vice versa

AND operator

• condition1 AND condition2 will evaluate to true if both conditions are true, else to false.

OR operator

• condition1 OR condition2 evaluates to true if condition1 is true or if condition2 is true or if both condition1 and condition2 are true, evaluates to false otherwise.

Selection Instructions

• IF (condition) { <block of statements> } executes the code in block of statements if the Boolean expression condition evaluates to true; otherwise it will take no action.
• IF (condition) { <first block of statements> } ELSE { <second block of statements> } executes the code in first block of statements if the Boolean expression condition evaluates to true; otherwise the code in second block of statements is executed.

Iteration Instructions

• REPEAT n TIMES { <block of statements> } executes the code in block of statements n times.
• REPEAT UNTIL (condition) { <block of statements> } executes the code in block of statements is repeated until the Boolean expression condition evaluates to true.

List Operations

• If a list index is less than 1 or greater than the length of the list, an error message is thrown
• list[i] refers to the element of list at index i. The first element of list is at index 1.
• list[i] ← list[j] assigns the value of list[j] to list[i].
• list ← [value1, value2, value3] will assign value1, value2, and value3 to list[1], list[2],and list[3],respectively.
• FOR EACH item IN list { <block of statements> } assigns the value of each element of list to the variable item sequentially, in order from the first element to the last, and th code in block of statements is executed once for each assignment of item.
• INSERT (list, i, value) shifts values in list at indices equal or greater than i to the right. The length of list is increased by 1, and value is placed at index i in list.
• APPEND (list, value) increases the length of list by 1, and value is placed at the end of list.
• REMOVE (list, i) removes the item at index i in list and shifts to the left any values at indices greater than i. Length of list is decreased by 1.
• LENGTH (list) will find the number of elements in list.

Procedures

• PROCEDURE name (parameter1, parameter2, ...){ <instructions> } A procedure, name, takes zero or more parameters and and contains programming instructions.
• PROCEDURE name (parameter1, parameter2, ...) { <instructions> RETURN (expression) } contains programming insructions and returns the value of expression, and the RETURN statement will cause an return back to the calling program.

Robot instructions

• MOVE_FORWARD () will move the robot one square forward in the direction it is facing and if it attempts to move to a square will stay if it is beyond the edge of the grid and the program will terminate.
• ROTATE_LEFT () will rotate the robot 90 degrees counterclockwise (i.e., makes an in-place left turn) and if it attempts to move to a square will stay if it is beyond the edge of the grid and the program will terminate.
• ROTATE_RIGHT () will rotate the robot 90 degrees clockwise (i.e., makes an in-place right turn) and if it attempts to move to a square will stay if it is beyond the edge of the grid and the program will terminate.
• CAN_MOVE (direction) evaluates to true if there is an open square one square in the direction relative to where the robot is facing; otherwise evaluates to false, with direction can be left, right, forward, or backward and it attempts to move to a square will stay if it is beyond the edge of the grid and the program will terminate.