Thread: Evaluate mathematical expression

i am currently writing a program that is meant to evaluate a mathematical expression of the form a*b-c*d-f . This expression can be of any length and possibly of float variables.

however, my piece of code is meant to evaluate only about two variables and not more... So i need help with a loop that can evaluate an expression of any length.

Code:

//here is my code


#include <stdio.h>
#include <stdlib.h>

int main(void)
{
     int s;
     char op;
     float exp1, exp2, sum = 0;
     printf ("\nThis program evaluates a mathematical expression of any length.");
      printf("\nEnter 'Q' to exit.");
     
     for ( ; ; )
     {
         printf("\nEnter Expression: ");
        while(getchar() != '\n')
        {
             s = scanf(" %f %c %f", &exp1,op,exp2);
              getchar(); // i don't however feel comfortable putting //getchar here... i need help with this loop
             if ( s != 3)
             {
                 printf("\nExiting...");
                 exit(EXIT_SUCCESS);
             }
             
             if ( op == '+') sum += exp1 + exp2;
             else if ( op == '-') sum += exp1 - exp2;
             else if ( op == '/') sum += exp1 / exp2;
             else if ( op == '*') sum += exp1 * exp2;

           }
           printf("\nExpression: %.2f", sum);
        }
        return 0;
}

//this code may run only for two expressions and not more....

For complicated expressions that contain any number of sub expressions, I think you'd have to compile the string containing the expressions into an abstract syntax tree. Then once you've done that, evaluate sub expressions from the bottom of the tree up, passing the results into the containing expression until you've reached the root of the tree.

Abstract syntax tree - Wikipedia, the free encyclopedia

yes i agree @antred but i have been explicitely restricted to either use getchar or scanf with loops to solve the problems without using either arrays or trees..... any way i'll check that page on wiki to see what it gives.

however @laserlight the assignment requires that you can evaluate an infinite number of expressions in so far as it is input correctly i think using a while loop can go but however @stahta01 parentheses arenot permitted only the integers of floats with the respective operators.

however@laserlight. this program uses the first come first some operator style whereby the the expression is evaluated as it is entered, i was thinking of using a while loo p to evaluate the expression using getchar() but this function stores the ascii code and not the integer. so this kinda complicates the expression.

@laserlight i think using a variable from getchar() directly on printf gives something different from expected. when i verified i saw getchar stored the ascii code of the variable and not the variable making computation difficult.

I don't think using getchar() is the best choice in your case (you have to process floats, haven't you?).
What's wrong with using scanf()?

Bye, Andreas