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CS157 HW2: Digraphs                

Description                

For this assignment, you will write a program called dg.c (a “digraph” is a pair of letters). It will read any number of files, and emit a report about the frequency of letter pairs in the input.                 

Sample Runs                

Here are several sample runs. Your output must match exactly, except that the order of the output lines may vary.                 

    % cat data
    Mama misses
    Papa
    % c11 -Wall dg.c
    % ./a.out 1 999 data
    ma 2
    am 1
    mi 1
    is 1
    ss 1
    se 1
    es 1
    pa 2
    ap 1
    % cat f
    food
    % cat d
    dood
    % ./a.out 1 99 f d
    fo 1
    oo 2
    od 2
    do 1
    % ./a.out 1 99 d f
    do 1
    oo 2
    od 2
    fo 1
    % cat hitch
      Don't
    Panic!
    % ./a.out 1 1000 hitch
    do 1
    on 1
    pa 1
    an 1
    ni 1
    ic 1
    % cat now
    2026-02-12T18:59:37.131071
    % ./a.out 1 1000 now
    % ./a.out 1500 1000000 ~cs157/pub/hamlet.txt
    ha 1891
    at 1523
    er 2105
    in 1951
    th 3947
    he 2991
    an 1995
    nd 1536
    or 1593
    ou 1941
    % ./a.out 1600 2000 ~cs157/pub/hamlet.txt
    ha 1891
    in 1951
    an 1995
    ou 1941

Required Data Structures                

Your program must create an array of this type in main, and use it to hold the data throughout the program:                 

    struct LetterPair {		// Note the capital L & P.
        char first, second;
        int count;
    };

• You may not change struct LetterPair in any way.
• The struct LetterPair type should be declared outside of any function.
• The array must be declared inside of main.

    export STACK_FRAME_LINK_OVERRIDE=ffff-ad921d60486366258809553a3db49a4a

Requirements                

• The first two arguments are the inclusive range letter pairs. That is, if the range is 15 17 then only display digraphs if their count is 15, 16, or 17.
• Produce an error message if:
  • minimum or maximum isn’t a number
  • the minimum count is less than one
  • the maximum count is less than the minimum count (equal is ok)
  • not enough arguments are given (there must be at least one file)
  • an unopenable file is given. The message must include the bad file name.
• Error messages must contain argv[0] and go to standard error. Then, terminate the program—no digraph counts should be produced.
• “Letter” means the 26 English letters A…Z or a…z.
• Treat all letters, upper or lower case, as if they were lower case.
• It doesn’t matter in what order your program emits the lines.
  • We will test your program by piping the output through sort -nk2
• Each input line will be no more than 93 characters long.
• There is no limit to the number of input lines. None!
• You open a file, you close it.
• You may not use global variables (global constants, types, and #defines are fine).
  • However, you may have a single global string representing the program name, for error messages.
• Use char constants for char values, not int ASCII values: 'A', not 65.

How to submit your homework:                

Use web checkin, or:                 

    ~cs157/bin/checkin HW2 dg.c

How to receive negative points:                

Turn in someone else’s work.                 

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