/****************************************************

  CPSC 211
  Author: Teresa Leyk

 Complex numbers, adding and multiplying complex numbers,
 reading in complex numbers (interactively or from a file).

 If we read from a file we use the following convention:
 * complex numbers are represented as pairs of double numbers
 * after this pair goes an operation code:
   1 for adding
   2 for multiplication
 * end of file ends reading in.
 * after each pair read in we print out the result.

 We assume that interactively we enter only one complex pair.
 The result is printed on output.

 *****************************************************/

#include <stdio.h>

/*** complex type ***/

typedef struct {
  double re, im;
} Complex;


/*** operations on complex numbers ***/

Complex complex_add(Complex a, Complex b)
{
  Complex c;
  
  c.re = a.re + b.re;
  c.im = a.im + b.im;
  return c;
}

Complex complex_mult(Complex a, Complex b)
{
  Complex c;

  c.re = a.re*b.re - a.im*b.im;
  c.im = a.re*b.im + a.im*b.re;
  return c;
}

Complex read_complex_number(FILE *fp)
{
  double re, im;
  Complex a;

  fscanf (fp," %lf %lf",&re, &im);
  a.re = re;
  a.im = im;
  return a;
}


/*** some constants ***/

typedef enum {
  Quit = 0, Interactively, FromFile
} Reading_mode;

typedef enum {
  None = 0, Add = 1, Multiply = 2
} Operation_mode;

/*** choose reading mode:
     1 - interactively
     2 - from a file
     check correctness of entered mode
***/
void choose_reading(Reading_mode *rm)
{
  int i;

  printf("\n\nChoose reading mode:\n"
	 "1. interactively\n"
	 "2. from a file\n"
	 "0. quit\n\n");
  scanf(" %d", &i);
  if (i < 0 || i > 2) {
    printf("ERROR: wrong choice: %d\n\n",i);
    exit(1);
  }
  *rm = i; 
}

/*** choose operation mode:
     1 - adding
     2 - multiplying
     check correctness of entered mode
***/
void choose_operation(Operation_mode *op)
{
  int i;
  
  printf("\n\nChoose operation:\n"
	 "1. adding\n"
	 "2. multiplying\n\n");
  scanf(" %d", &i);
  if (i < 1 || i > 2) {
    printf("ERROR: wrong choice: %d\n\n",i);
    exit(1);
  }
  *op = i;
}

Operation_mode read_operation(FILE *fp)
{
  int i;

  fscanf(fp, " %d",&i);
  if (i < 0 || i > 2) {
    printf("ERROR: wrong operation: %d\n\n",i);
    exit(1);
  }
  return i;
}

/*** get a file name ***/
void choose_file_name(FILE **fp)
{
  char name[50];

  printf("Enter file name:\n");
  scanf(" %49s", name);
  *fp = fopen(name, "r");
  if (*fp == NULL) {  
    printf("ERROR: the file \"%s\" cannot be open\n\n", name);
    exit(1);
  }
}

/* nice print-out */
void print_operation(Operation_mode op, Complex a, Complex b,
		     Complex c)
{
  char op_char;

  switch (op) {
  case None: return;
  case Add: op_char = '+'; break;
  case Multiply: op_char = '*'; break;
  }

  printf("(%g, %g) %c (%g, %g) = (%g, %g)\n",
	 a.re, a.im, op_char, b.re, b.im, c.re, c.im);

}


void read_numbers_from_file(void)
{
  FILE *fp;
  Complex a, b, c;
  Operation_mode op;

  choose_file_name(&fp);
  while (!feof(fp)) {
    a = read_complex_number(fp);
    b = read_complex_number(fp);
    /* read operation */
    op = read_operation(fp);
    printf("Result is:\n");
    switch (op) {
    case None: 
      printf("End of file\n");
      return;
    case Add:
      c = complex_add(a,b);
      print_operation(op, a, b, c);
      break;
    case Multiply:
      c = complex_mult(a, b);
      print_operation(op, a, b, c);
      break;
    }
    printf("\n");
  }
}


void read_numbers_interactively(void)
{
  Complex a, b, c;
  Operation_mode op;

  printf("Enter the first complex number (pair of real numbers): \n");
  a = read_complex_number(stdin);
  printf("Enter the second complex number (pair of real numbers): \n");
  b = read_complex_number(stdin);
  choose_operation(&op);
  printf("\nResult is:\n");
  switch (op) {
  case None: return;
  case Add:
    c = complex_add(a,b);
    print_operation(op, a, b, c);
    break;
  case Multiply:
    c = complex_mult(a, b);
    print_operation(op, a, b, c);
    break;
  }
  printf("\n\n");
}

void menu(void)
{
  Reading_mode rm;
  
  choose_reading(&rm);
  
  switch (rm) {
  case Quit: exit(0);
  case Interactively:
    read_numbers_interactively();
    break;
  case FromFile:
    read_numbers_from_file();
    break;
  }

}

int main(void)
{
  while (1)  /* infinite loop */ 
    menu();
}