Code

 Header...
//
// Find the impedance of an electrical circuit
 //

#define INFINITY 1e100
#define PI 3.14159265358979

typedef enum type{Resistor,Capacitor,Inductor,Series,Parallel}Type;

typedef struct component {
  double value;
  Type type;
  unsigned int n;// If parallel or serial
  struct component *nodes[];// If parallel or serial
}Component;

 Component* newcomponent(void){
   ... 

»  char *names[]={"Resistor","Capacitor","Inductor","Series","Parallel",NULL};
»  Component *c=NULL;
»  Type type;
»  int n;

»  while (1) {
»    printf("What type of component?\n");
»    for ( int i=0;namesi!=NULL; ++i) 
      printf("%d\t%s\n", i, namesi);
    
»    scanf("%d", &type);
»    switch (type) {
»    case Resistor:
»    case Capacitor:
»    case Inductor:
»      c=xmalloc(sizeof *c);
»      c->type=type;
»      while (1) {
»        printf("Please enter the value of the %s\n", names(c->type));
»        scanf("%lg", &c->value);
»        if (c->value>0) 
          return c;
»        printf("Please enter a positive value\n");
  }

»    case Series:
»    case Parallel:
»      while (1) {
»        printf("How many nodes are there?\n");
»        scanf("%ud", &n);
»        if (n>0) 
          break;
»        printf("Please enter a positive value\n");
  }

»      c=xmalloc(sizeof *c+n*sizeof *c->nodes);
»      c->n=n;
»      for (n=0; n<c->n; ++n) 
        c->nodesn=newcomponent();
»      return c;

»    default :
»      printf("Sorry \"%d\" is not a valid option, please try again\n", 
             c->type);

}
  }
}

 double complex impedance(Component *c,double freq){
   ... 

»  double complex z=0;
»  double denom;

»  switch (c->type) {
»  case Resistor:
»    return c->value;

»  case Inductor:
»    return 2*PI*I*c->value*freq;

»  case Capacitor:
    // Handle DC and v low frequencies
»    denom=2*PI*c->value*freq;
»    if (denom<1.0/INFINITY) 
     denom=1.0/INFINITY;
»    return 1.0/(I*denom);

»  case Series:
»    for ( int n=0;n<c->n; ++n) 
      z+=impedance(c->nodes[n], freq);
»    return z;

»  case Parallel:
»    for ( int n=0;n<c->n; ++n) 
      z+=1.0/impedance(c->nodes[n], freq);
»    return 1.0/z;
  }
}

 int main(){
   ... 

»  Component *c=NULL;
»  double complex z;
  
»  c=newcomponent();
»  z=impedance(c, 50000);
»  printf("The impedance is:\n"
         "\tmodulus %g and phase %g\n", 
         cabs(z), carg(z));
         
»  return 0;
}

Where two numbers are shown the first is the real part, the second the imaginary.