2.2
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What is a variable?
• Value stored in memory that can change while the program is running
What is a constant?
• Value that does not change while the program is running • Assigned when the program is designed
What is assignment?
• Giving a variable/constant a value
What is casting?
• Converting a variable from one data type to another • integer/character/string/float/boolean
What is an input?
• Value read from an input device (e.g. keyboard)
What is an output?
• Data generated by the computer • Displayed to the user
What does ** mean?
• Exponential
What does % mean?
• Modulus (remainder)
What does // mean?
• Quotient
What are the boolean operators?
• AND: both must be true (D logic gate with two inputs one output) • OR: either must be true (fish/kite logic gate with two inputs one output) • NOT: false (triangle with tip pointing right at a small dot with one input one output)
Why is casting necessary?
• Softwares receive data in a format they are expecting • Manipulation of data
What are the 3 stages to writing data to a file?
• variable = open(‘filename.txt’, ‘a’) to append (OR to write do ‘w’) • variable.writeLines • \n = enter a new line • variable.close()
What are the 3 stages to reading data from a file?
• variable = open(‘filename.txt’, ‘r’) to read • variable2 = variable.readline() • print(variable2) • To read next line, just do another variable and do variable.readline() again
Why do you need to close a file?
• Releases the file handle and breaks the connection between it and program • variable.close()
What do you have to do once you have written to a file but want to read it (or vice versa)?
• variable = open(‘filename.txt’, ‘r’) to read • variable = open(‘filename.txt’, ‘a’) to append (OR to write do ‘w’) • MUST do before cause that is just file handling rule
SQL Commands
• SELECT: field to be returned (* = all) • FROM: which file • WHERE: certain condition (LIKE = wildcard) • ORDER BY: ASC or DESC
Explain the two main types of sub programs
• Procedures: carry out a task and provide structure to code (basically main.py) • Functions: carry out a task and return a value, creating reusable program components
What are the advantages of subroutines?
• Easier to write entire program (many can work on large program at the same time, cutting down development time) • Easier to debug (maintainability: can be tested separately) • Reusable components (could be gathered into library for use over multiple programs) • Good programming technique
What is a record?
• Collection of related data items for one entity (could be different data types)
What are records stored in text files?
• Stored on secondary storage • Used to store data when the application if closed • Each entry is on a new line • May require linear search to find data • Structure text files (e.g. CSV) can be used to exchange stored data between applications
What are records stored in arrays/lists?
• Stored in main memory (RAM) • Used to store data when program is running • Single/multi-dimensional • Indexes refer to data items • Efficient algorithms are used to find data
What is the difference between an array and list?
• Array: static data structure (1D) • List: dynamic data structure (2D)
What are the three basic programming constructs?
• Sequence: executing one instruction after another, one by one • Selection: a program branch depending on a condition (IF) • Iteration: repeating code in a loop (counter (FOR)/condition (WHILE)) until a condition has been satisfied
What are the advantages of local variables?
• Self-contained within subroutine, can be used without variable names conflicting with those used in main (if a local and global variable have the same name, the local variable takes priority within the function • Memory efficient: memory space is created when the subroutine is executing, it will be released when the execution is finished