Complex number arithmetic

cmplx.c

/* Pre-processor directive */
#include <stdio.h>
#include <math.h>
					    /*Type def */
typedef struct
{
  float real;
  float imag;
} complex;
					    /* Function prototypes */
int mainMenu ();
complex inputComplexNumbers_first ();
complex inputComplexNumbers_second ();
complex addTwoComplexNumbers (complex a, complex b);
complex subTwoComplexNumbers (complex a, complex b);
complex multwoComplexNumbers (complex a, complex b);
int
main (void)
{
  int theirchoice;

  complex numberchoice_first, numberchoice_second;

  complex sumcomplex, diffComplex, multComplex;




  while (-1)			/* While loop, only to terminate when commanded or wrong twice */
    {
      theirchoice = mainMenu ();	/* Function call 'mainMenu()' */
      if (theirchoice == 1)
	{

	  numberchoice_first = inputComplexNumbers_first ();
	  numberchoice_second = inputComplexNumbers_second ();
	  sumcomplex =
	    addTwoComplexNumbers (numberchoice_first, numberchoice_second);
	  printf ("\n Sum of two complex numbers is: %f %f \n\n", sumcomplex.real, sumcomplex.imag);

	}

      else if (theirchoice == 2)
	{

	  numberchoice_first = inputComplexNumbers_first ();
	  numberchoice_second = inputComplexNumbers_second ();
	  diffComplex =
	    subTwoComplexNumbers (numberchoice_first, numberchoice_second);
	  printf ("\n Difference of the two complex numbers is: %f %f \n",
		  diffComplex.real, diffComplex.imag);

	}

      else if (theirchoice == 3)
	{
	  numberchoice_first = inputComplexNumbers_first ();
	  numberchoice_second = inputComplexNumbers_second ();
	  multComplex =
	    multwoComplexNumbers (numberchoice_first, numberchoice_second);
	  printf ("\n Multiplication of the two complex numers is: %f %f \n",
		  multComplex.real, multComplex.imag);

	}

      else if (theirchoice == 4)
	{

	  exit (0);

	}
    }
  return (0);
}

int
mainMenu ()
{
  int numberchoice;
  printf ("----------Menu----------\n");
  printf ("1 Add two complex numbers\n");
  printf ("2 Subtract two complex numbers\n");
  printf ("3 Multiply two complex numbers\n");
  printf ("4 Exit the program\n");
  printf ("Please select an option (1, 2, 3, or 4): ");
  scanf ("%d", &numberchoice);
  printf ("\n\n");

  if ((numberchoice >= 5) || (numberchoice <= 0))	/* If statement repeats if choice is wrong */
    {
      printf ("Invalid number choice, retry. \n\n\n:");


      printf ("----------Menu----------\n");
      printf ("1 Add two complex numbers\n");
      printf ("2 Subtract two complex numbers\n");
      printf ("3 Multiply two complex numbers\n");
      printf ("4 Exit the program\n");
      printf ("Please select an option (1, 2, 3, or 4): ");
      scanf ("%*[^\n]");	/* To remove their invalid characters */
      scanf ("%*1[\n]");
      scanf ("%d", &numberchoice);
      printf ("\n\n");

      if ((numberchoice >= 5) || (numberchoice <= 0))
	{
	  printf ("Invalid entry, program will now close. \n\n");
	  exit (0);		/* Exits program when entered incorrectly twice */
	}
      else
	return (numberchoice);

    }

  return (numberchoice);
}

complex
inputComplexNumbers_first () /* Function definition */
{
  complex a;
  printf (" \n Enter the first set of  numbers in the format a b: ");
  scanf ("%f %f", &a.real, &a.imag);

  return (a);			/* Suspect that it isn't scanning or returning correctly, however i cannot find a solution */
}

complex
inputComplexNumbers_second ()
{
  complex b;
  printf (" \n Enter the second set of numbers numbers in the format a b: ");
  scanf ("%f %f", &b.real, &b.imag);

  return (b);			/* Suspect that it isn't returning correctly, however i cannot find a solution */
}

complex
addTwoComplexNumbers (complex a, complex b)
{
  complex c;
  c.real = a.real + b.real;	/* Isn't adding correctly due to suspected error in scanning */
  c.imag = a.imag + b.imag;

  return (c);
}

complex
subTwoComplexNumbers (complex a, complex b)
{
  complex c;
  c.real = (a.real - b.real);	/* Isn't subracting correctly due to suspected error in scanning */
  c.imag = (a.imag - b.imag);

  return (c);
}

complex
multwoComplexNumbers (complex a, complex b)
{
  complex c;
  c.real = (a.real * b.real) - (a.imag * b.imag);	/* Isn't multiplying correctly due to suspected error in scanning */
  c.imag = (a.imag * b.real) + (a.real * b.imag);

  return (c);
}