declaring complex numbers in C language

The most basic way would be to create a struct defining each component of the number. Assuming you are only working in 1 dimension then your complex number will be of the form ai+b, and so your struct would look like

typedef struct {
    float a; //The "imaginary" part. Might be a int instead
    float b; //The real part. Might be a int instead
} ComplexNumber;

Could you please provide the equation and indicate weather it needs to work on other similar equations or only this exact one and the operations that you are wanting to perform.
If it is a relatively simple equation like sqrt(-1) then there can be a simple answer without having to implement a complex numbers system.

ComplexNumber ComplexSqrt(float nNumber) {
    ComplexNumber cnRes = { 0, 0 };
    if (nNumber < 0) { //nNumber is negative. Result will be complex
        cnRes.a = sqrt(-nNumber);
    } else { //nNumber is positive. Result will be real
        cnRes.b = sqrt(nNumber);
    }
    return cnRes;
}

Thanks Andrew for your response.
However the equation that i am reffering to as given below:

"Qen[n1]=exp(j*(n1-1)*(vv0[k]-vv0[l]))"

This expression is the one that i need to calculate and the concern is how to remove the 'j' part from the equation.

Looking forward to your further replies ..

cheers
Setu

If you consider the complex number in the form of a+bi and like to look a code in C# then here it is. You can use operator overloading to perform arithmatic operations with complex numbers

class ComplexNumber
{
    public double Number1{ get; set;}
    public double Number2{ get; set;}
    public double ImaginaryUnit { get; set; }
    public ComplexNumber()
    {

    }
    public ComplexNumber(double number1, double number2, double imaginaryUnit)
    {
        this.Number1 = number1;
        this.Number2 = number2;
        this.ImaginaryUnit = imaginaryUnit;
    }

    public static ComplexNumber operator +(ComplexNumber Number1, ComplexNumber Number2)
    {
        ComplexNumber number = new ComplexNumber();
        number.Number1 = Number1.Number1 + Number2.Number1 ;
        number.Number2 = Number1.Number2 + Number2.Number2;
        number.ImaginaryUnit = Number1.ImaginaryUnit;
        return number;
    }

    public static ComplexNumber operator -(ComplexNumber Number1, ComplexNumber Number2)
    {
        ComplexNumber number = new ComplexNumber();
        number.Number1 = Number1.Number1 - Number2.Number1;
        number.Number2 = Number1.Number2 - Number2.Number2;
        number.ImaginaryUnit = Number1.ImaginaryUnit;
        return number;
    }
    public static ComplexNumber operator *(ComplexNumber Number1, ComplexNumber Number2)
    {
        double ac = Number1.Number1 * Number2.Number1;
        double bd = Number1.Number2 * Number2.Number2;
        double bc = Number1.Number2 * Number2.Number1;
        double ad = Number1.Number1 * Number2.Number2;
        double result = (ac - bd) + ((bc + ad) * Number1.ImaginaryUnit);
        ComplexNumber number = new ComplexNumber();
        number.Number1 = ac-bd;
        number.Number2 = bc-ad;
        number.ImaginaryUnit = Number1.ImaginaryUnit;
        return number;
    }

    public static ComplexNumber operator /(ComplexNumber Number1, ComplexNumber Number2)
    {
        double square = 2;
        double ac=Number1.Number1 * Number2.Number1;
        double bd=Number1.Number2 * Number2.Number2;
        double bc=Number1.Number2 * Number2.Number1;
        double ad=Number1.Number1 * Number2.Number2;

        double c2=System.Math.Pow(Number2.Number1, square);
        double d2=System.Math.Pow(Number2.Number2, square);
        ComplexNumber number = new ComplexNumber();
        number.Number1 = (ac + bd) / (c2 + d2);
        number.Number2 = (bc - ad) / (c2 + d2);
        number.ImaginaryUnit = Number1.ImaginaryUnit;
        return number;
    }
}