I am quite new to programming. This is in relation to python. So the idea is to take an expression such as 3/5 or, at most, 3/5*2(at most two operators, note that the operators can be any of +,-,/,*) and solve it. White space can exist anywhere within the expression.
The user enters the expression, say 3/5, and the program needs to solve the expression and display the answers. What I have tried is below. Note, I only have attempted the first part, once I can properly split the original expression that the user enters(which would be a string), creating functions would be the easy part:
expres= str(input("something:"))
ssplit= hit.partition("/")
onec= int((ssplit[0].lstrip()).rstrip())
twoc= (ssplit[1].lstrip()).rstrip()
threec= int((huns[2].lstrip()).rstrip())
print(onec,"...",twoc,"...",threec) #just a debug test print
So above, I can take an expression like 3/5 and split it into three separate strings:3 , /, and 5. I can also remove all whitespace before and after the operators/operands. I am having problems with splitting expressions like 4/5+6, Because I can't put code in for ssplit[3] or ssplit[4] and then enter an expression like 3/5, because it won't be defined. Basically I needed you help to find out how to split an expression like 3/4-6,etc. I also need help with the line "ssplit= hit.partition("/")" so that it will look at the entered expression and work with +,-, and * as well. Any and all help is appreciated. Also if my code above looks nasty and inefficient please give me criticism. Thanks!
Note I can't, and wouldn't want to use eval. Order of operations is required. I cant use complicated commands. I need to keep it simple, the most I can use is string libraries, converting between strings/integers/floats etc. and if,and,etc. statements. I can also use functions.
If I wasn't going to rely on external libraries, I'd do it something like this:
def parse(x):
operators = set('+-*/')
op_out = [] #This holds the operators that are found in the string (left to right)
num_out = [] #this holds the non-operators that are found in the string (left to right)
buff = []
for c in x: #examine 1 character at a time
if c in operators:
#found an operator. Everything we've accumulated in `buff` is
#a single "number". Join it together and put it in `num_out`.
num_out.append(''.join(buff))
buff = []
op_out.append(c)
else:
#not an operator. Just accumulate this character in buff.
buff.append(c)
num_out.append(''.join(buff))
return num_out,op_out
print parse('3/2*15')
It's not the most elegant, but it gets you the pieces in a reasonable data structure (as far as I'm concerned anyway)
Now code to actually parse and evaluate the numbers -- This will do everything in floating point, but would be easy enough to change ...
import operator
def my_eval(nums,ops):
nums = list(nums)
ops = list(ops)
operator_order = ('*/','+-') #precedence from left to right. operators at same index have same precendece.
#map operators to functions.
op_dict = {'*':operator.mul,
'/':operator.div,
'+':operator.add,
'-':operator.sub}
Value = None
for op in operator_order: #Loop over precedence levels
while any(o in ops for o in op): #Operator with this precedence level exists
idx,oo = next((i,o) for i,o in enumerate(ops) if o in op) #Next operator with this precedence
ops.pop(idx) #remove this operator from the operator list
values = map(float,nums[idx:idx+2]) #here I just assume float for everything
value = op_dict[oo](*values)
nums[idx:idx+2] = [value] #clear out those indices
return nums[0]
print my_eval(*parse('3/2*15'))