Potential Pointer issue C programming - c

Question

I've been working through this problem, and I believe I have an error in where my pointers within my struct are pointing. However, I can't seem to figure out where I'm going wrong.
My code is meant to take in 2 complex numbers, then multiply and divide them, and then spit out both answers.
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
struct complex_t
{
double real; // real part
double imag; // imaginary part
} complex_t;
// Multiplication Function //
void *multiply()
{
struct complex_t a, b, c;
c.real == ((a.real * b.real) - (a.imag * b.imag));
c.imag == ((a.imag * b.real) + (a.real * b.imag));
if ( c.imag >= 0 )
printf("Multiplication = %d + %di\n", c.real, c.imag); // Postive Imaginary case
else
printf("Multiplication = %d %di\n", c.real, c.imag); // Negative Imaginary case
}
// Division Function //
void *divide()
{
int numer1, numer2, denom;
struct complex_t a, b, c;
if ( b.real == 0 || b.imag == 0 ) // Case to Avoid Dividing by 0
printf("Division by 0 + 0i is not allowed.");
else
{
numer1 = ((a.real * b.real) + (a.imag * b.imag));
numer2 = ((a.imag * b.real) - (a.real * b.imag));
denom = ((b.real * b.real) + (b.imag * b.imag));
c.real == (numer1/denom);
c.imag == (numer2/denom);
if (numer2/denom >= 0)
printf("Division = %d + %di \n", c.real, c.imag); // Postive Imaginary case
else
printf("Division = %d %di \n", c.real, c.imag); // Negative imaginary case
}
}
// Main - to execute the two functions //
int main() {
struct complex_t a, b, c;
printf("Enter a and b where a + ib, for the first complex number.");
printf("\na = ");
scanf("%d", &a.real);
printf("b = ");
scanf("%d", &a.imag);
printf("Enter c and d where c + id, for the second complex number.");
printf("\nc = ");
scanf("%d", &b.real);
printf("d = ");
scanf("%d", &b.imag);
multiply();
divide();
return 0;
}
This is an example of what this program is producing:
Multiplication = 69144 -4196352i
Division = -13339222 0i
Any tips as to where I can start figuring this error out would be great.

Answer 1

C is an exact language. There is no such thing as syntax that is close enough. This is a great strength in C, but it is one hurdle beginning programmers have to come to terms with and understand before any real learning can take place. That includes understanding what each part of each line does, including the format strings. If you don't fully understand what each part of each line is doing -- look it up. Read the man pages, search for further information, until you do. It will save you a ton of time in the long run.
One of the things you can do that will, above all, help you find the problems in your code is to compile with Warnings enabled. That means including at least -Wall -Wextra in your compile string. For example, in your code, the screen was littered with warnings, including code with no apparent function and expected double but have int. Those things are telling you, you can try and run your code -- but DO NOT expect it to work right. You have to fix those, before you can have reasonable confidence that you will get more than garbage (or a crash) out of your code.
Another primary bit of learning that must take place is Always initialize your variables (to zero if nothing else). Attempting to access an uninitialized variable is Undefined Behavior. (it's anybody's guess what will happen.)
That being said. You had part of the code right. Your issues basically took slowing down, reading what the compiler was telling you was wrong, fixing it, and trying again. That's the key to C, slow down and get it right.
Enough blather -- are you going to help or not? Of course. Read through the following. Understand why the changes were necessary, and you will be able to consider it a good bit of learning for the day. However, the fixes in the code below, are not near as important as the guidance above for approaching C programming. (give a man a fish....):
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
typedef struct {
double real; // real part
double imag; // imaginary part
} complex_t;
// Multiplication Function //
void multiply (complex_t *a, complex_t *b, complex_t *c) {
/* struct complex_t a, b, c; */
c->real = ((a->real * b->real) - (a->imag * b->imag));
c->imag = ((a->imag * b->real) + (a->real * b->imag));
if (c->imag >= 0)
printf ("\nMultiplication = %f + %fi\n", c->real, c->imag); // Postive Imaginary case
else
printf ("\nMultiplication = %f %fi\n", c->real, c->imag); // Negative Imaginary case
}
// Division Function //
void divide (complex_t *a, complex_t *b, complex_t *c) {
int numer1, numer2, denom;
/* struct complex_t a, b, c; */
if (b->real == 0 || b->imag == 0) // Case to Avoid Dividing by 0
printf ("Division by 0 + 0i is not allowed.");
else {
numer1 = ((a->real * b->real) + (a->imag * b->imag));
numer2 = ((a->imag * b->real) - (a->real * b->imag));
denom = ((b->real * b->real) + (b->imag * b->imag));
c->real = (numer1 / denom);
c->imag = (numer2 / denom);
if (numer2 / denom >= 0)
printf ("\nDivision = %f + %fi \n", c->real, c->imag); // Postive Imaginary case
else
printf ("\nDivision = %f %fi \n", c->real, c->imag); // Negative imaginary case
}
}
// Main - to execute the two functions //
int main () {
complex_t a = { 0, 0 }, b = { 0, 0 }, c = { 0, 0 };
printf ("\nEnter a and b where a + ib, for the first complex number.\n\n");
printf (" a (a.real) = ");
scanf ("%lf", &a.real);
printf (" b (a.imag) = ");
scanf ("%lf", &a.imag);
printf ("\nEnter c and d where c + id, for the second complex number.\n\n");
printf (" c (b.real) = ");
scanf ("%lf", &b.real);
printf (" d (b.imag) = ");
scanf ("%lf", &b.imag);
multiply (&a, &b, &c);
divide (&a, &b, &c);
printf ("\n");
return 0;
}
output:
$ ./bin/divmult
Enter a and b where a + ib, for the first complex number.
a (a.real) = 10
b (a.imag) = 3
Enter c and d where c + id, for the second complex number.
c (b.real) = 5
d (b.imag) = 5
Multiplication = 35.000000 + 65.000000i
Division = 1.000000 + 0.000000i

Answer 2

void *multiply()
The values of struct variables a and b are not initialized within this function you should be passing the scanned values in main() to this function as well as divide()
There is no reason here I see why you are returning void *. Pass parameters by reference or by value.