Cộng,trừ,nhân,chia hai số phức

#include<stdio.h>
#include<conio.h>
#include<math.h>
#include<stdlib.h>

void in(float a, float b);
void cong(float a1, float a2,float b1, float b2, float &a, float &b);
void tru(float a1, float a2,float b1, float b2, float &a, float &b);
void nhan(float a1, float a2,float b1, float b2, float &a, float &b);
void chia(float a1, float a2,float b1, float b2, float &a, float &b);

main()
{
float a1,a2,b1,b2,a3,b3,a4,b4,a5,b5,a6,b6;
int tL;

lap:
printf("So thu nhat: \n ")  ;
printf("Phan thuc: ");
scanf("%f",&a1);
printf("Phan ao: ");
scanf("%f",&b1);
printf("So thu hai: \n");
printf("Phan thuc: ");
scanf("%f",&a2);
printf("Phan ao: ");
scanf("%f",&b2);
system("cls");

tinh:
printf("1: Phep cong so thuc \n");
printf("2: Phep tru so thuc \n");
printf("3: Phep nhan so thuc \n");
printf("4: Phep chia so thuc \n");
printf("Moi ban chon ");
scanf("%d",&tL);

switch(tL)
    {
        case 1:
            cong(a1,b1,a2,b2,a3,b3);
            in(a3,b3);
            break;
        case 2:
            tru(a1,b1,a2,b2,a4,b4);
            in(a4,b4);
            break;
        case 3:
            nhan(a1,b1,a2,b2,a5,b5);
            in(a5,b5);
            break;
        case 4:
            chia(a1,b1,a2,b2,a6,b6);
            in(a6,b6);
            break;
    }

    printf("Moi ban lua chon \n");
    printf("1: Nhap bo so moi\n");
    printf("2: Thuc hien lai phep toan\n");
    printf("So khac ket thuc\n");
    scanf("%d",&tL);

    switch(tL)
    {
        case 1:
            goto lap;
        case 2:
            goto tinh;
        default:;
    }
}

void in(float a, float b)
{
    printf("%.2f",a);
    if(b<0)
    {

    }
    else
    printf(" +");
    printf(" %.2fi \n",b);
}

void cong(float a1,float a2,float b1, float b2, float &a, float &b)
{
    a = a1 + a2;
    b = b1 + b2;

}

void tru(float a1,float a2,float b1, float b2, float &a, float &b)
{
    a = a1 - a2;
    b = b1 - b2;

}

void nhan(float a1,float a2,float b1, float b2, float &a, float &b)
{
    a = a1*a2 - b1*b2;
    b =a1*b2 + a2*b1;

}

void chia(float a1,float a2,float b1, float b2, float &a, float &b)
{
    a = (a1*a2 + b1*b2)/(a2*a2 + b2*b2);
    b = (a2*b1 - a1*b2)/(a2*a2 + b2*b2);

}