sum complex numbers in function with a variable number of parameters

Question

I want to sum X complex numbers, but this code returns me:

-9.3e+61 + -1.9e+062i

typedef struct complex{
    double real;
    double imag;
} complex;

complex sum(int length, ...)
{
    va_list param;
    va_start(param, length);

    complex out = {0, 0};
    for(int i = 0;i<length;i++)
    {
        out.real += va_arg(param, complex).real;
        out.imag += va_arg(param, complex).imag;
    }
    va_end(param);
    return out;
}

when i quote real / imag part in for, it returns right real / imag result.

main:

int main()
{
    complex result;
    complex a = {3.1,-2.3};
    complex b = {0.5,-3};
    complex c = {0,1.2};

    result = sum(3,a,b,c);
    printf("Sum is %.2g + %.2gi. \n", result.real, result.imag);

    return 0;
}

What should i change to make it works?

Answer 1

The problem is that every time you call va_arg , it will take out one whole complex struct. Since you call it twice per loop, you take out 2 different complex struct, which is incorrect.

You need to cache the result and access the members later:

for (int i = 0; i < length; i++)
{
    complex currArg = va_arg(param, complex);
    out.real += currArg.real;
    out.imag += currArg.imag;
}