## Ruby mode

# Code from http://sandbox.mc.edu/~bennet/ruby/code/poly_rb.html # # This program evaluates polynomials. It first asks for the coefficients # of a polynomial, which must be entered on one line, highest-order first. # It then requests values of x and will compute the value of the poly for # each x. It will repeatly ask for x values, unless you the user enters # a blank line. It that case, it will ask for another polynomial. If the # user types quit for either input, the program immediately exits. # # # Function to evaluate a polynomial at x. The polynomial is given # as a list of coefficients, from the greatest to the least. def polyval(x, coef) sum = 0 coef = coef.clone # Don't want to destroy the original while true sum += coef.shift # Add and remove the next coef break if coef.empty? # If no more, done entirely. sum *= x # This happens the right number of times. end return sum end # # Function to read a line containing a list of integers and return # them as an array of integers. If the string conversion fails, it # throws TypeError. If the input line is the word 'quit', then it # converts it to an end-of-file exception def readints(prompt) # Read a line print prompt line = readline.chomp raise EOFError.new if line == 'quit' # You can also use a real EOF. # Go through each item on the line, converting each one and adding it # to retval. retval = [ ] for str in line.split(/\s+/) if str =~ /^\-?\d+$/ retval.push(str.to_i) else raise TypeError.new end end return retval end # # Take a coeff and an exponent and return the string representation, ignoring # the sign of the coefficient. def term_to_str(coef, exp) ret = "" # Show coeff, unless it's 1 or at the right coef = coef.abs ret = coef.to_s unless coef == 1 && exp > 0 ret += "x" if exp > 0 # x if exponent not 0 ret += "^" + exp.to_s if exp > 1 # ^exponent, if > 1. return ret end # # Create a string of the polynomial in sort-of-readable form. def polystr(p) # Get the exponent of first coefficient, plus 1. exp = p.length # Assign exponents to each term, making pairs of coeff and exponent, # Then get rid of the zero terms. p = (p.map { |c| exp -= 1; [ c, exp ] }).select { |p| p[0] != 0 } # If there's nothing left, it's a zero return "0" if p.empty? # *** Now p is a non-empty list of [ coef, exponent ] pairs. *** # Convert the first term, preceded by a "-" if it's negative. result = (if p[0][0] < 0 then "-" else "" end) + term_to_str(*p[0]) # Convert the rest of the terms, in each case adding the appropriate # + or - separating them. for term in p[1...p.length] # Add the separator then the rep. of the term. result +=( if term[0] < 0 then " - " else " + " end) + term_to_str(*term) end return result end # # Run until some kind of endfile. begin # Repeat until an exception or quit gets us out. while true # Read a poly until it works. An EOF will except out of the # program. print "\n" begin poly=r eadints( "Enter a polynomial coefficients: ") rescue TypeError print "Try again.\n" retry end break if poly.empty? # Read and evaluate x values until the user types a blank line. # Again, an EOF will except out of the pgm. while true # Request an integer. print "Enter x value or blank line: " x=r eadline.chomp break if x=='' raise EOFError.new if x=='quit' # If it looks bad, let 's try again. if x !~ /^\-?\d+$/ print "That doesn't look like an integer. Please try again.\n " next end # Convert to an integer and print the result. x = x.to_i print "p(x)=", polystr(poly), " \n " print "p( ", x, ")=", polyval(x, poly), " \n " end end rescue EOFError print "\n===E OF===\n " rescue Interrupt, SignalException print "\n===I nterrupted===\n " else print "--- Bye ---\n " end

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