ช่วยโค้ด ภาษา c ให้น่อยครับ

#include"stdio.h"
#include"conio.h"
#include "stdlib.h"
main()
{
float a,b,c,d;
b>0;
d>0;
d=b*100;
c>0;
c=(a/(d*d));
printf("BMI Cale\n");
printf("\n");
printf("Enter your weight in kg.");
printf("\n");
scanf("%f",&a);
printf("\n");
printf("Enter your height in cm.");
printf("\n");
scanf("%f",&b);
printf("\n");
printf("Your BMI is ");
printf("%f",c);
printf("\n");
printf("\n");
if((c<=0))printf("error");
if((a<=0))printf("error");
if((b<=0))printf("error");
if((d<=0))printf("error");
if((c<18.5)&&(c>10))printf("Your Is Underweight");
if((c>=18.5)&&(c<25)) printf("Your Is Normal");
if((c>=25)&&(c<30))printf("Your Is Overweight");
if((c>=30))printf("Your Is Obese");
printf("\n");

    printf("\n");
    printf("enter key to exit \n");
    getche();
    return 0;





}