#include<stdio.h>
#include<conio.h>
void main()
{
float l,b,a;
clrscr();
printf("Enter length:\n");
scanf("%f",&l);
printf("Enter breadth:\n");
scanf("%f",&b);
a=l*b;
printf("Area of rectangle=%f",a);
getch();
}

Sample Run:
Enter length:
5
Enter breadth:
10
Area of rectangle=50.000000