Circuit Analysis code snippet

/*====================================
    Equivalent Resistance
====================================*/
//Series and Parallel Topologies
double get_effective_resistance(double restarr[], int topology, int resist_no){
    double effective_resistance = 0.0;
    int i;
    double placeholder = 0.0;
    if(topology==1){
        for(i=0; i<resist_no; i++){
            placeholder += restarr[i];
        }
        effective_resistance = placeholder;
    }else if(topology==2){
        for(i=0; i<resist_no; i++ ){
            placeholder += (1/restarr[i]);
        }
        effective_resistance = placeholder;
    }else if(topology==3){
        printf("ResistNO. @case3\n",resist_no);
        effective_resistance = get_ladder_resistance(restarr,resist_no);
    }else{
        printf("Error in Function \"get_effective_resistance\" in file \"circuit.c\"");
        return -1;
    }
    return effective_resistance;
}

//Ladder Topology
double get_ladder_resistance(double restarr[], int resist_no){
    double x = 0.0;
    int i = resist_no;
    int placeholder = 0;
    //printf("DEBUGLADDER: 1\n");
    while(i>=0){
      //      printf("DEBUGLADDER: 2\n");
      printf("DEBUGladder: %d\n",i);
        if(i<3||i%3==0){
        //    printf("DEBUGLADDER: 3\n");
            placeholder = i-3;
            printf("DebugPH: %d\n", placeholder);
            do{
          //      printf("DEBUGLADDER: 4\n");
                x += restarr[i-1];
            //    printf("DEBUGLADDER: 5\n");
                i--;
                printf("DEBUGLADDER: 6\n");

            }while(i>placeholder);
            continue;
            //printf("DEBUGLADDER: 7\n");
        }else if(i%3==2){
            //printf("DEBUGLADDER: 3.1\n");
            placeholder = i-2;
            do{
             //   printf("DEBUGLADDER: 4.1\n");
                x += restarr[i-1];
               // printf("DEBUGLADDER: 5.1\n");
                i--;
               // printf("DEBUGLADDER: 6.1\n");
            }while(i>=placeholder);
            //printf("DEBUGLADDER: 7.1\n");
            continue;
        }else{
            //printf("DEBUGLADDER: 8\n");
            if(i==resist_no){
                x = (restarr[i-1]*restarr[i-2])/(restarr[i-1]+restarr[i-2]);
                printf("DEBUGLADDER: 8.1:%d\n",restarr[i-2]);
            }else{
                x = (x*restarr[i-2])/(x+restarr[i-2]);
                printf("DEBUGLADDER: 8.2\n");
            }
            //printf("DEBUGLADDER: 9\n");
            i--;
            printf("DEBUGLADDER: 10:%.6f\n",x);
            continue;
        }
        //printf("DEBUGLADDER: 11");
    }
    //printf("DEBUGLADDER: 12");
    double y = x;
    //printf("DEBUGLADDER: 13");
    return y;
}