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/***************************************************
F = m a Program

Write a program that solves for the unknown variable
in the F = m a equation.  The user enters two
variable = value pairs (e.g "m = 10.0 F = 3.5") and
the program writes the unknown variable and its
value ("a = .35" in our example).

***************************************************/
#include "si204.h"

/* Note: this is the straightfoward but very TEDIOUS
 * way to solve this problem. */
int main() {
  fputs("The F = m a Program\n", stdout);

  // Read first variable/value pair
  char var1;
  char c;
  double val1;
  fputs("Enter <var> = <value> : ", stdout);
  var1 = readchar(stdin); // the variable
  c = readchar(stdin);    // the equals sign
  val1 = readnum(stdin);  // the value

  // Read second variable/value pair
  char var2;
  double val2;
  fputs("Enter <var> = <value> : ", stdout);
  var2 = readchar(stdin); // the variable
  c = readchar(stdin);    // the equals sign
  val2 = readnum(stdin);  // the value

  // Decide which variable is missing & solve
  if (var1 == 'F') {   
    // var1 is F
    if (var2 == 'm') {
      fputs("a = ", stdout);
      writenum(val1 / val2, stdout);
      fputs("\n", stdout);
    } else {
      fputs("m = ", stdout);
      writenum(val1 / val2, stdout);
      fputs("\n", stdout);
    }
  } else {
    if (var1 == 'm') {
      // var1 is m
      if (var2 == 'a') {
        fputs("F = ", stdout);
        writenum(val1 * val2, stdout);
        fputs("\n", stdout);
      } else {
        fputs("a = ", stdout);
        writenum(val2 / val1, stdout);
        fputs("\n", stdout);
      }
    } else {  
      // var1 is a
      if (var2 == 'm') {
        fputs("F = ", stdout);
        writenum(val1 * val2, stdout);
        fputs("\n", stdout);
      } else {
        fputs("m = ", stdout);
        writenum(val2 / val1, stdout);
        fputs("\n", stdout);
      }
    }
  }
 
 return 0;
}