computer science paper 1

Algorithm

• Variables of this type remain in memory even when a subroutine ends, their scope is the whole program
• A statement that assigns a value to a variable. The right side of the equals sign can be any expression. These are valid: health ← 100 fare ← 5 + 0.5 * miles
• A sequence of steps that can be followed to complete a task.
• A type of translator which converts a high-level language in to machine code all at once

Decomposition

• Precise, English-like description of an algorithm. It has no specific syntax, so input name and if name is bob are valid instructions.
• Boolean operator that returns a true value only if both operands are true
• Breaking a problem into a number of sub-problems, so that each sub- problem accomplishes an identifiable task, which might itself be further subdivided.
• This translator converts a high-level language into machine code one line at a time and then executes it, it's slower but interpreted code is quicker to write and easier to update

Abstraction

• Programing languages designed to make it easier for humans to understand and write computer programs, than using low-level languages. Examples include Python and C#.
• Coding a second programming construct inside the first. You can do this with selection and iteration
• A collection of related data items called fields, often stored as a row in a database, it represents something in the real world like a person or product
• The process of removing unnecessary detail from a problem.

Pseudo-code

• The numeric value of a character in a the character set. In ASCII, "A" is 65
• Programing languages designed to make it easier for humans to understand and write computer programs, than using low-level languages. Examples include Python and C#.
• A statement that assigns a value to a variable. The right side of the equals sign can be any expression. These are valid: health ← 100 fare ← 5 + 0.5 * miles
• Precise, English-like description of an algorithm. It has no specific syntax, so input name and if name is bob are valid instructions.

Flowchart

• Boolean operator that returns a true value only if both operands are true
• A programming construct where the code makes a decision, and takes one of several branches, usually coded with IF-THEN-ELSE
• This statement starts a condition-controlled loop with the condition at the start, so the loop will only begin if the condition is true
• A visual representation of an algorithm using specific shapes including rectangle, diamond and parallelogram.

IPO

• Breaking a problem into a number of sub-problems, so that each sub- problem accomplishes an identifiable task, which might itself be further subdivided.
• Where inputs, processing and outputs are taking place within an algorithm.
• A sequence of steps that can be followed to complete a task.
• The process of removing unnecessary detail from a problem.

Linear search

• A data type also called floating point numbers, they have a decimal part, for example 1.5, 0.935 or the value of Pi
• A searching algorithm which looks at every element in turn until it finds the target, it is slow but works even on unsorted data
• Boolean operator that returns a true value only if both operands are true
• The systematic process of running a program repeatedly with different input data and checking the output is as expected, revealing errors

Binary search

• It cannot change. A named memory location for something that stays the same. Examples are PI, Number_of_Levels, MAXHEALTH
• A searching algorithm that divides the search space in half each time until it finds the target, faster than linear but requires the array to be sorted
• Variables of this type remain in memory even when a subroutine ends, their scope is the whole program
• A programming construct where the code makes a decision, and takes one of several branches, usually coded with IF-THEN-ELSE

Merge sort

• A low-level language which uses mnemonics such as LDA, ADD to represent machine code instructions
• A subroutine which does not return a value. For example it might redraw the screen or write a record to a file
• A very efficient sorting algorithm that repeatedly breaks down a list into smaller lists, then repeatedly merges them back together in order
• Programing languages designed to make it easier for humans to understand and write computer programs, than using low-level languages. Examples include Python and C#.

Bubble sort

• A sorting algorithm that passes over the list many times, swapping adjacent items if they are in the wrong order. Not very efficient.
• A function in pseudo-code that returns part of a string when we pass it a starting position and length
• An error that occurs when code runs but produces unexpected results. E.g. adding instead of subtracting or stopping a loop too soon. It is detected by systematic testing with a trace table
• A searching algorithm that divides the search space in half each time until it finds the target, faster than linear but requires the array to be sorted