How can i sum complex numbers? Need help with this exercise!

**peppeNzjik** · 06-26-2012

Hello, I just need help with this exercise:
So Z1=5+3i
and Z2=-2-5i

The sum is 3-2i. But how can I print it? The code i wrote here prints me 3 4198924 i. What am I doing wrong?

Code:

#include <stdio.h>

int a,b,c,d;
int COMPSUM(int a,int b,int c,int d);

int main()
{
    //int a,b,c,d;
    printf("Enter first complex number real part:\n");
    scanf("%d\n",&a);
    printf("Enter first complex number imaginary part:\n");
    scanf("%d\n",&b);
    printf("Enter second complex number real part:\n");
    scanf("%d\n",&c);
    printf("Enter second complex number imaginary part:\n");
    scanf("%d\n",&d);
    printf("%d %d i\n",COMPSUM(a,b,c,d));
    return 0;
}
int COMPSUM(int a,int b,int c,int d){
    int e,f;
    e=a+c;
    f=b+d;
    return e,f;
}

**hk_mp5kpdw** · 06-26-2012

A return statement can only return a single value, a complex number is represented by two values. In order to return a complex number as a single value, you would need to wrap up the two components in a struct and return a struct representing the sum. Then, you would still be unable to print as you are doing since can't print a struct in C (you could in C++ with operator overloading). You would have to print the elements of the struct individually which would most likely mean storing the sum into a temporary of some kind and then passing the two components of the temporary to the printf call.

Start with this:

Code:

struct complex
{
    int real;
    int imaginary;
};

int main()
{
    struct complex first, second, sum;

    /* Get real/imaginary values into first, second struct */

    /* Compute sum and store into sum struct */

    /* Print the sum struct's real/imaginary components */

    return 0;
}

**ledow** · 06-26-2012

Code:

return e,f;

Wrong, wrong, wrong, wrong, wrong.

You cannot return two answers in the return value of a function, and you certainly can't do it using the "," operator.

Similarly, you can't use a printf with two %d's and then give it only the SINGLE return value that will come out of COMPSUM. That's why you get junk.

**ledow** · 06-26-2012

P.S. ENABLE WARNINGS ON YOUR COMPILER!

(I really get sick of telling people that).

It would have spotted both problems for you immediately:

..\test.c: In function 'main':
..\test.c:17: warning: too few arguments for format
..\test.c: In function 'COMPSUM':
..\test.c:24: warning: left-hand operand of comma expression has no effect

**Tibo-88** · 06-26-2012

You cannot return multiple parameters from a function in C. You need either to return a struct that will contain both numbers, or use a sum function two times, one for each part.

**peppeNzjik** · 06-26-2012

Code:

#include <stdio.h>

typedef struct Complex {
    float real;
    float img;
} Complex;

Complex complex_sum (Complex z1, Complex z2) {
    Complex z3;
    z3.real = z1.real + z2.real;
    z3.img = z1.img + z2.img;
    return z3;
}
int main()
{
    Complex z1, z2, z3;

    printf("Enter first complex number\n");
    printf("Enter complex number real part:\n");
    scanf("%f\n", &z1.real); //here I enter 5
        printf("Enter complex number imaginary part:\n");
        scanf("%f\n", &z1.img); //here I enter 3

printf("Enter second complex number\n");
    printf("Enter complex number real part:\n");
    scanf("%f\n", &z2.real); //here I enter -2
    printf("Enter complex number imaginary part:\n");
    scanf("%f\n", &z2.img); //here I enter -5

    z3 = complex_sum(z1, z2);
    //Show sum

printf("Sum: %f + i*%f", z3.real, z3.img);
    getchar();
    return 0;
}

I get no error messages or warnings, but it prints me 3.000000 + i*3.000000.

**hk_mp5kpdw** · 06-26-2012

Code:

scanf("%f\n", &z1.real);

Get rid of all those \n parts, they don't belong.

**peppeNzjik** · 06-26-2012

I figured it out, thanks to you. It works now. Thank You.

**Subsonics** · 06-26-2012

As a side note, C99 added native support for complex numbers with complex.h.

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