Question

Function which takes a string and uses a stack to calculate the value of theequation passed in. This equation is assumed to be in postfix/reverse Polishnotation.

RETURNS: The value that the equation evaluates to using postfix notation

python please :)

Answer 1

Here is the python code to given question.

Sample outputs are added at the end.

Code:

#create stack class
class stack:
    
    
    #initialize stack
    def __init__(self):
        
        self.stackList=[]
        self.top=-1
    
    
    #pushes value into stack
    def push(self,value):
        
        self.stackList.append(value)   #appends value into stack
        self.top+=1       #increments top by 1
    
    
    #pops the element at top of stack
    def pop(self):
        
        if self.top!=-1:        #checks if stack is not empty
            
            self.top-=1        #decrements the value of top by 1
            return self.stackList.pop()     #returns the top element of stack
          
          
          
#function to evaluate postfix expression  
def evaluatePostfix(expression):
    
    expressionList=expression.split(' ')     #converts string words to list
    
    stackObject=stack()      #creates a new stack object
    
    for i in expressionList:
        
        if i.isdigit():       #checks if i is a number
            
            stackObject.push(int(i))      #pushes the number into top of stack
        
        else:
            
            value1=stackObject.pop()      #pops element at top of stack
            
            value2=stackObject.pop()      #pops element at top of stack
            
            if i=='+':
                
                stackObject.push(int(value2+value1))     #pushes value2+value1 into the stack
            
            elif i=='-':
    
                stackObject.push(int(value2-value1))        #pushes value2-value1 into the stack
            
            elif i=='*': 
                
                stackObject.push(int(value2*value1))       #pushes value2*value1 into the stack
            
            elif i=='/':
                
                 stackObject.push(int(value2/value1))      #pushes value2/value1 into the stack
            
            elif i=='^':
                
                stackObject.push(int(value2**value1))    #pushes value2**value1 into the stack
            
    return stackObject.pop()    #returns top element of stack


def main():
    
    inputExpression=input("Enter postfix expression: ")    #takes input expression from user
    
    print(evaluatePostfix(inputExpression))     #calls evaluatePostfix method and prints the value returned
    
if __name__=="__main__":
    
    main()    #calls main
    
    
      

Sample output-1:

Sample output-2: