Data is entered from the user by using the scanf() function.  The scanf() function reads in integers, floating-point variables, and characters.  The format string for the scanf() function is:  

scanf(" format string ", arguments );

The format string includes type-specifiers that instruct scanf() how to interpret key characters.  Here are the scanf() type-specifiers, which will be introduced at this time:  

• "%c" - Reads a single character
• "%d" - Reads a signed integer (int) numbers ( white space is used to separate multiple numbers )
• "%ld" - Reads long signed integers (long int)
• "%hd" - Reads short-signed integers ( short int)
• "%hu" - Reads unsigned short integer( unsigned short int ) integers
• "%u" - Reads unsigned integer (unsigned int) numbers
• "%f", "%e", "%E" - Reads a single-precision floating-point number
• "%lf", "%le", "%lee" - Reads a double-precision floating-point number
• "%Lf", "%Le", "%LE" - Reads a floating-point number of the long double

/* area.c
*/

#include<stdio.h>
#include<conio.h>

main()
{
    double area, length, width;

    printf("Enter a length--> ");
    scanf("%lf", &length);

    printf("Enter a width--> ");
    scanf("%lf", &width);

    area = length * width;

    printf("\n\nThe length is %lf and the width is %lf.", length, width);
    printf("\nThe area is %lf. ", area);

    getch();
    return 0;
}