A-level Computing/AQA/Paper 1/Skeleton program/AS2020

This is the AQA Computer Science Paper 1 discussion page, please do not vandalise the page as students use this for revision. Be sensible. Respect the page.

Possible questions based on the current ASCII Art scenario:

Change Display Error sub routine to allow "codes"

Change the display error subroutine to allow text error messages to replaced by codes. For extensions you may add alternative or new error codes.

Python:

def DisplayError(ErrorMessage_code):
  Error_messages = ["Image Data Error", "File not found error", "unknown error"]
  print("Error: ", Error_messages[ErrorMessage_code])


def LoadFile(Grid, Header):
  FileFound = False
  FileTypeOK = False
  FileName = input("Enter filename to load: ")
  try:
    FileIn = open(FileName + ".txt", 'r')
    FileFound = True
    HeaderLine = FileIn.readline()
    Fields = HeaderLine.split(',')
    Header.Title = Fields[0]
    Header.Width = int(Fields[1])
    Header.Height = int(Fields[2])
    Header.FileType = Fields[3]
    Header.FileType = Header.FileType[0]
    if Header.FileType == 'A':  
      Grid = LoadAsciiImage(FileIn, Grid, Header)
      FileTypeOK = True
    elif Header.FileType == 'G': 
      Grid = LoadGreyScaleImage(FileIn, Grid, Header)
      FileTypeOK = True
    FileIn.close()
    if not FileTypeOK:
      '''DisplayError(2)'''
    else:
      DisplayImage(Grid, Header)
  except:
    if not FileFound:
      '''DisplayError(2)'''
    else:
      '''DisplayError(2)'''
  return Grid, Header

Java:

  void displayError(int errorcode) {
        String[] errors = new String[] {"Image Data Error","Unknown File Type","File not found", "Unknown Error"};
        Console.writeLine("Error: " + errors[errorcode]);
    }

void loadFile(String[][] grid, FileHeader header) {
        boolean fileFound = false;
        boolean fileTypeOK = false;
        Console.write("Enter filename to load: ");
        String fileName = Console.readLine();
        try {
            BufferedReader fileIn = new BufferedReader(new FileReader(fileName + ".txt"));
            fileFound = true;
            String headerLine = fileIn.readLine();
            String[] fields = headerLine.split(",");
            header.title = fields[0];
            header.width = Integer.parseInt(fields[1]);
            header.height = Integer.parseInt(fields[2]);
            header.fileType = fields[3];
            header.fileType = header.fileType.charAt(0) + "";
            if (header.fileType.equals("A")) { 
                loadAsciiImage(fileIn, grid, header);
                fileTypeOK = true;
            } else if ( header.fileType.equals("G")){
                loadGreyScaleImage(fileIn, grid, header);
                fileTypeOK = true;
            }
            fileIn.close();
            if (!fileTypeOK) {
                displayError(1); /// error code
            } else {
                displayImage(grid, header);
            }
        } catch (IOException e) {
            if (!fileFound) {
                displayError(1);  // error code
            } else {
                displayError(2);  // error code
            }
        }
    }

Give the option to enlarge image

Add another menu option to scale up an image as specified by the user.

Python:

def enlarge (Grid, Header):

  scale = int(input('Please enter scale 2 and above'))

  NewGrid = [['' for Column in range(Header.Width*scale)] for Row in range(Header.Height * scale)]

  for Row in range(Header.Height):
    for count1 in range(scale):
      for Column in range(Header.Width):
        for count2 in range(scale):
          NewGrid[(Row*scale)+count1][(Column*scale)+count2] = Grid[Row][Column]


  Header.Width = Header.Width * scale
  Header.Height = Header.Height * scale
  return NewGrid, Header

def DisplayMenu():
  print()
  print("Main Menu")
  print("=========")
  print("L - Load graphics file") 
  print("D - Display image")
  print("E - Edit image")
  print("S - Save image")
  print("C - Scale file")
  print("X - Exit program") 
  print()

def Graphics():
  Grid = [['' for Column in range(MAX_WIDTH)] for Row in range(MAX_HEIGHT)]
  Grid = ClearGrid(Grid)
  Header = FileHeader()
  ProgramEnd = False
  while not ProgramEnd:
    DisplayMenu()
    MenuOption = GetMenuOption()
    if MenuOption == 'L':
      Grid, Header = LoadFile(Grid, Header)
    elif MenuOption == 'D':
      DisplayImage(Grid, Header) 
    elif MenuOption == 'E':
      Grid = EditImage(Grid, Header) 
    elif MenuOption == 'S':    
      SaveImage(Grid, Header)
    elif MenuOption == 'C':
      print(Header.Width)
      Grid, Header = enlarge(Grid, Header)
      print (Header.Width)
    elif MenuOption == 'X':
      ProgramEnd = True
    else:
      print("You did not choose a valid menu option. Try again")
  print("You have chosen to exit the program")
  Answer = input("Do you want to save the image as a graphics file? (Y/N) ")
  if Answer == "Y" or Answer == "y":
    SaveFile(Grid, Header)

Saving Image as ASCII or Graphics

Change the SaveFile subroutine to allow Graphics or ASCII files to be saved.

Python:

def SaveFile(Grid, Header):
  FileName = input("Enter filename: ")
  FileOut = open(FileName + ".txt", 'w')
  FileOut.write(Header.Title + ',' + str(Header.Width) + ',' + str(Header.Height) + ',' + Header.FileType + '\n')  ### added Header.FileType
  for Row in range(Header.Height):
    for Column in range(Header.Width):
      if Header.FileType == 'A':
        FileOut.write(Grid[Row][Column])
      else:
        FileOut.write(convertInteger(Grid[Row][Column])) ### created subroutine to convert "ASCII" into "INTEGER GRAPHCICS", only work if ASCII characters not changed. Use ASCII Values?
        FileOut.write('\n')

  FileOut.close()


def convertInteger(char):
  if char == '#':
    PixelValue = 32
  elif char =='&':
    PixelValue = 64
  elif char == "+":
    PixelValue = 96
  elif char == ";":
    PixelValue = 128
  elif char == ":":
    PixelValue = 160
  elif char == ",":
    PixelValue = 192
  elif char == ".":
    PixelValue = 224
  else:
    PixelValue = 255
  return PixelValue

Java:

   void saveFile(String[][] grid, FileHeader header) {
        Console.write("Enter filename: ");
        String fileName = Console.readLine();
        try {
            BufferedWriter fileOut = new BufferedWriter(new FileWriter(fileName + ".txt"));
            fileOut.write(header.title + "," + header.width + "," + header.height + "," + header.fileType + "\n");
            for (int row = 0; row < header.height; row++) {
                for (int column = 0; column < header.width; column++) {
                    if (header.fileType == "A") {
                        fileOut.write(grid[row][column]);
                    } else {
                        fileOut.write(convertInteger(grid[row][column]));
                    }
                    fileOut.write(grid[row][column]);
                }
            }
            fileOut.close();            
        } catch (IOException e) {
        }
    }

    int convertInteger(String character) {
        String characters = "#&+;,:,. ";
        int PixelValue = 32 * (characters.indexOf(character)+1);   // returns character position
        return PixelValue;
    }

Save Compressed images using RLE

Add option to save file as a compressed ASCII image. Adds another filetype

Python:

def compressFile(Grid, Header):
  Header.FileType = "C"
  FileName = input("Enter filename: ")
  FileOut = open(FileName + ".txt", 'w')
  FileOut.write(Header.Title + ',' + str(Header.Width) + ',' + str(Header.Height) + ',' + Header.FileType + '\n')

  for Row in range(Header.Height):
    pre_char = ''
    counter = 1
    temp = ''
    for Column in range(Header.Width):
      if Grid[Row][Column] != pre_char:
        if pre_char:
          temp = temp + str(counter) + pre_char
        counter = 1
        pre_char = Grid[Row][Column]
      else:
        counter = counter + 1
    temp = temp + str(counter) + pre_char
    FileOut.write(temp)
    FileOut.write('\n')

Load Compressed Image

In Load subroutine pickup compressed file type and load into GRID

Python:

def LoadFile(Grid, Header):
  FileFound = False
  FileTypeOK = False
  FileName = input("Enter filename to load: ")
  try:
    FileIn = open(FileName + ".txt", 'r')
    FileFound = True
    HeaderLine = FileIn.readline()
    Fields = HeaderLine.split(',')
    Header.Title = Fields[0]
    Header.Width = int(Fields[1])
    Header.Height = int(Fields[2])
    Header.FileType = Fields[3]
    Header.FileType = Header.FileType[0]
    if Header.FileType == 'A':  
      Grid = LoadAsciiImage(FileIn, Grid, Header)
      FileTypeOK = True
    elif Header.FileType == 'G': 
      Grid = LoadGreyScaleImage(FileIn, Grid, Header)
      FileTypeOK = True
    elif Header.FileType == 'C':  ### add extra filetype
      Grid = LoadCompressedFile(FileIn, Grid, Header)
      FileTypeOK = True

    FileIn.close()
    if not FileTypeOK:
      DisplayError(2)
    else:
      DisplayImage(Grid, Header)
  except:
    if not FileFound:
      DisplayError(2)
    else:
      DisplayError(2)
  return Grid, Header

def LoadCompressedFile(FileIn, Grid, Header):
  count = ''
  NextChar = 0
  for Row in range(Header.Height):
    ImageData = FileIn.readline()
    temp = ''
    column = 0
    NextChar = 0
    Grid[Row]=[]
    while column < Header.Width:
      if ImageData[NextChar].isdigit():
        count = count + ImageData[NextChar]
      else:

        Grid[Row] = Grid[Row] + ([ImageData[NextChar]] * int(count))
        column = column + int(count)
        count = ""
      NextChar = NextChar + 1


  return Grid

Validate change symbol

In the editImage subroutine add a function to validate whether the chosen symbol to replace exists in current image. Create SymbolExist subroutine which returns a boolean values of TRUE or FALSE depending whether given symbol exists in image.

Java:

  void editImage(String[][] grid, FileHeader header) {
        displayImage(grid, header);
        String answer = EMPTY_STRING;
        while (!answer.equals("N")) {
            String symbol = EMPTY_STRING;
            String newSymbol = EMPTY_STRING;
            while (symbol.length() != 1) {
                boolean valid = false;
                while (!valid) {   /// added loop to enforce validation
                    Console.write("Enter the symbol you want to replace: ");
                    symbol = Console.readLine();
                    valid = symbol_exist(symbol, grid, header);
                    if (!valid) {
                        Console.write("Symbol doesn't exist");
                    }
                }
            }
            while (newSymbol.length() != 1) {
                Console.write("Enter the new symbol: ");
                newSymbol = Console.readLine();
            }
            for (int thisRow = 0; thisRow < header.height; thisRow++) {
                for (int thisColumn = 0; thisColumn < header.width; thisColumn++) {
                    if (grid[thisRow][thisColumn].equals(symbol)) {
                        grid[thisRow][thisColumn] = newSymbol;
                    }
                }
            }
            displayImage(grid, header);
            Console.write("Do you want to make any further changes? (Y/N) ");
            answer = Console.readLine();
        }
    }

  boolean symbol_exist(String symbol, String[][] grid, FileHeader header){
        boolean found = false;

        for (int thisRow = 0; thisRow < header.height; thisRow++) {
            for (int thisColumn = 0; thisColumn < header.width; thisColumn++) {
                if (grid[thisRow][thisColumn].equals(symbol)) {
                   found = true;
                }
            }
        }
        return found;
    }

Validate change symbol (Python)

In the editImage subroutine add a function to validate whether the chosen symbol to replace exists in current image. Create SymbolExist subroutine which returns a boolean values of TRUE or FALSE depending whether given symbol exists in image.

Python:

def EditImage(Grid, Header):
  DisplayImage(Grid, Header)
  Answer = EMPTY_STRING
  while Answer != "N":
    Symbol = EMPTY_STRING
    NewSymbol = EMPTY_STRING
    while len(Symbol) != 1:
      Symbol = input("Enter the symbol you want to replace: ")
      valid = SymbolExist(Symbol, Grid, Header)
      if valid != True:
        Symbol = ''
        print("Symbol not found, please try again")
    while len(NewSymbol) != 1:
      NewSymbol = input("Enter the new symbol: ")
    for ThisRow in range(Header.Height):
      for ThisColumn in range(Header.Width):
        if Grid[ThisRow][ThisColumn] == Symbol:
          Grid[ThisRow][ThisColumn] = NewSymbol
    DisplayImage(Grid, Header)
    Answer = input("Do you want to make any further changes? (Y/N) ")
  return Grid


def SymbolExist(Symbol, Grid, Header):
    for ThisRow in range(Header.Height):
      for ThisColumn in range(Header.Width):
        if Grid[ThisRow][ThisColumn] == Symbol:
          return True
    return False