#
# 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+$/
retval.push(str.to_i)
else
raise TypeError.new
end
end
return retval
end
#
# Take a coeff and an exponent and return the string representation, ignoring
# the sign of the coefficient.
def term_to_str(coef, exp)
ret = ""
# Show coeff, unless it's 1 or at the right
coef = coef.abs
ret = coef.to_s unless coef == 1 && exp > 0
ret += "x" if exp > 0 # x if exponent not 0
ret += "^" + exp.to_s if exp > 1 # ^exponent, if > 1.
return ret
end
#
# Create a string of the polynomial in sort-of-readable form.
def polystr(p)
# Get the exponent of first coefficient, plus 1.
exp = p.length
# Assign exponents to each term, making pairs of coeff and exponent,
# Then get rid of the zero terms.
p = (p.map { |c| exp -= 1; [ c, exp ] }).select { |p| p[0] != 0 }
# If there's nothing left, it's a zero
return "0" if p.empty?
# *** Now p is a non-empty list of [ coef, exponent ] pairs. ***
# Convert the first term, preceded by a "-" if it's negative.
result = (if p[0][0] < 0 then "-" else "" end) + term_to_str(*p[0])
# Convert the rest of the terms, in each case adding the appropriate
# + or - separating them.
for term in p[1...p.length]
# Add the separator then the rep. of the term.
result += (if term[0] < 0 then " - " else " + " end) +
term_to_str(*term)
end
return result
end
#
# Run until some kind of endfile.
begin
# Repeat until an exception or quit gets us out.
while true
# Read a poly until it works. An EOF will except out of the
# program.
print "\n"
begin
poly = readints("Enter a polynomial coefficients: ")
rescue TypeError
print "Try again.\n"
retry
end
break if poly.empty?
# Read and evaluate x values until the user types a blank line.
# Again, an EOF will except out of the pgm.
while true
# Request an integer.
print "Enter x value or blank line: "
x = readline.chomp
break if x == ''
raise EOFError.new if x == 'quit'
# If it looks bad, let's try again.
if x !~ /^\-?\d+$/
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=== EOF ===\n"
rescue Interrupt, SignalException
print "\n=== Interrupted ===\n"
else
print "--- Bye ---\n"
end