title: parsing of mathematical expressions
body: <p>(in c90) (linux)</p>
  
  <p>input:</p>
  
  <pre><code>sqrt(2 - sin(3*A/B)^2.5) + 0.5*(C*~(D) + 3.11 +B)
  a
  b   /*there are values for a,b,c,d */
  c
  d
  </code></pre>
  
  <p>input:</p>
  
  <pre><code>cos(2 - asin(3*A/B)^2.5) +cos(0.5*(C*~(D)) + 3.11 +B)
  a
  b   /*there are values for a,b,c,d */
  c
  d
  </code></pre>
  
  <p>input:</p>
  
  <pre><code>sqrt(2 - sin(3*A/B)^2.5)/(0.5*(C*~(D)) + sin(3.11) +ln(B))
   /*max lenght of formula is 250 characters*/
  a
  b   /*there are values for a,b,c,d */
  c   /*each variable with set of floating numbers*/
  d
  </code></pre>
  
  <p>As you can see infix formula in the input depends on user.
  My program will take a formula and n-tuples value.
  Then it calculate the results for each value of a,b,c and d.
  If you wonder I am saying ;outcome of program is graph.
  /<em>sometimes,I think i will take input and store in string.
  then another idea is arise " I should store formula in the struct"
  but ı don't know how I can construct 
  the code on the base of structure.</em>/  </p>
  
  <p>really, I don't know way how to store the formula in program code so that
  I can do my job.
  can you show me?</p>
  
  <pre><code>/* a,b,c,d is letters
   cos,sin,sqrt,ln is function*/
  </code></pre>