try yourself |run program

#include <stdio.h> 
#include <conio.h> 
void main(){ 
 double a; 
 clrscr();
 printf("Enter value of a: ");
 scanf("%lf",&a);/*  & is used before variable name when you want to read data*/
 printf("\n value of a = %lf",a);
 getch();
}

Program Output

Enter value of a: 4538.34 
value of a = 4538.340000