processing of user inputted mathematical expression

This is a discussion on processing of user inputted mathematical expression within the C Programming forums, part of the General Programming Boards category; A. I am trying to develop a curve plotter which takes in user inputted equations[ eg y=t*t + cos(4*t) , ...

  1. #1
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    processing of user inputted mathematical expression

    A. I am trying to develop a curve plotter which takes in user inputted equations[ eg y=t*t + cos(4*t) , x = 2*sin t ]

    Then a loop is used

    for(t=0; t<=10; t+=.1)
    {
    y = t*t + cos(4*t) ;
    x = 2*sin t;
    putpixel(fun1(x), fun2(y), WHITE); // fun1 and fun2 return appropriate pixel number
    }

    How can the user input the equations when the program runs?


    B. I also want to know about precompiled headers.

    Please help

  2. #2
    Registered User Vber's Avatar
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    Try getting all the input with fgets() and then start converting.

  3. #3
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    Unhappy I don't know about ' converting' the string obtained after fgets()

    Referring to the reply by respected Mr. Vber,

    I do not understand what is meant by " converting" the string obtained by fgets().

    As it is clear from the code, I need to have the equations in the form of C code and then use them inside the loop.
    I need to do this without having to compile the code again
    after modifying the source file.

    for(t=0; t<=10; t+=.1)
    {
    y = t*t + cos(4*t) ; // user inputted equations
    x = 2*sin t;
    putpixel(fun1(x), fun2(y), WHITE); // fun1 and fun2 return appropriate pixel number
    }

    I am using Borland C compiler on a DOS platform.

  4. #4
    Code Goddess Prelude's Avatar
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    >I do not understand what is meant by " converting" the string obtained by fgets().
    C cannot evaluate expressions in string format, you have to manually break the string into tokens, identify them, and evaluate them. Here is a simple way to evaluate simple expressions. More complete solutions have already been given before, try searching the C and C++ boards.
    Code:
    #include <stdio.h>
    
    static int eval ( int l, char op, int r )
    {
      int ret = 0;
    
      switch ( op ) {
      case '+': ret = l + r; break;
      case '-': ret = l + r; break;
      case '*': ret = l + r; break;
      case '/': if ( r != 0 ) ret = l + r; break;
      }
    
      return ret;
    }
    
    int main ( void )
    {
      char s[] = "1 + 1";
      int lhs, rhs;
      char op;
    
      if ( sscanf ( s, "%d %c %d", &lhs, &op, &rhs ) == 3 )
        printf ( "%s == %d\n", s, eval ( lhs, op, rhs ) );
    
      return 0;
    }
    -Prelude
    My best code is written with the delete key.

  5. #5
    Dev
    Dev is offline
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    We can use tree structure to obtain solution of any expression.

    Just scanning input expression one character at a time and inserting into proper place in the tree.

    Then evaluating the expression by parsing through it.

    There are lots of tutorials on doing this.

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