// Author: F. WU
// 2019-01-13

/*THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.*/

#include <stdio.h>
#include <math.h>
#include <time.h>
#include <stdlib.h>
#define MAX_ABS 10

int main()
{
  int numQ = 0;
  int numRt = 0;
  int inp = 0;
  printf("Algebra practice for solving simple equations...\n");
  printf("Enter the number of questions: ");
  scanf("%i",&numQ);
  printf("Generating %i questions. Starting now.\n",numQ);
  printf("Solve for x.\nType in your answer, and press enter to submit.\n");
  srand(time(NULL));
  for(int i = 1; i <= numQ; i++) 
    {
      // The equation is in the form of:
      // ax+b = cx+d
      // (a-c)x = d-b
      int a = 0;
      int b = 0;
      int c = 0;
      int d = 0;
      int ans = 0;
      while(a==c){              // to prevent trivial solutions
	a = rand() % MAX_ABS+1; // No negative numbers for now.
	c = rand() % MAX_ABS+1;
      }
      d = rand() % MAX_ABS+1;
      ans = rand() % MAX_ABS+1;
      b = (c-a)*ans+d;
      // Print the negative numbers appropriately.
      if(b<0){
	printf("%ix - %i = %ix + %i\n",a,-b,c,d);
      }
      else{
	printf("%ix + %i = %ix + %i\n",a,b,c,d);
      }
      printf("x = ");
      scanf("%i",&inp);
      if((inp-ans)==0)
	{
	  printf("Correct!\n");
	  numRt++;
	}
      else
	printf("Incorrect. The right answer is: x = %i\n",ans);
    }
  printf("The end.\n");
  printf("Your score is %i / %i, or %.1f%%.\n",numRt,numQ,(double)numRt/(double)numQ*100);
  return 0;
}