1. Variables have a type have an address (in memory) have a value
have a name (for now)

2. Variables - name
must start with a-z, A-Z ( _ allowed, but not recommended)
other characters may be a-z, A-Z, 0-9, _
upper case/lower case are not equal (i.e. ECE, ece, Ece, EcE, eCe would be five different variables)
max length is system dependent (usually at least 32)
unique-ness length usually at least 32

3. Variables - legal names
GrossPay
Carpet_Price
carpet_price
a_very_long_variable_name i
______strange___one_____
_ (not recommended)

4. Variables - legal names (but not recommended)
l (that's lower case L)
O (that's capitol O)
l1 (that's lower case L, and digit one)
O0Oll11 (oh,zero,oh,el,el,one,one)
_var (many system variables begin with _ )

5. Variables - declaring var name memory loc
main() { float hours; float payrate; float grosspay; int j;
hours ?
4278
payrate ?
427C
4280
grosspay ? j ?
4284

6. Variables - assigning varname = expression Declared variable
single variable on left side of =
expression
any legal expression
In general, the type of the declared variable (int, float, etc) and the resultant type of the expression should be the same.
Note this is not a requirement...BUT, you should be aware that you are changing types across the equals and understand the ramifications.

7. Variables - declaring var name memory loc
main() { float hours; float payrate; float grosspay; int j;
hours = 40.0;
hours
40.0
4278
payrate ?
427C
4280
grosspay ? j ?
4284

8. Variables - declaring var name memory loc
main() { float hours; float payrate; float grosspay; int j;
hours = 40.0;
payrate = 20.00;
hours
40.0
4278
payrate
20.0
427C
4280
grosspay ? j ?
4284

9. Variables - declaring var name memory loc
main() { float hours; float payrate; float grosspay; int j;
hours = 40.0;
payrate = 20.00;
grosspay = hours * payrate
hours
40.0
4278
payrate
20.0
427C
4280
grosspay
800.00 j ?
4284
note: referencing a variable only "reads" it (non-destructive). Assigning to a variable overwrites whatever was there (destructive).

10. Variables - declaring var name memory loc
main() { float hours; float payrate; float grosspay; int j;
hours = 40.0;
payrate = 20.00;
grosspay = hours * payrate
j = 5;
hours
40.0
4278
payrate
20.0
427C
4280
grosspay
800.00 j 5
4284
note: referencing a variable only "reads" it (non-destructive). Assigning to a variable overwrites whatever was there (destructive).

11. ECE 160 - Introduction to Computer Engineering I
02/09/2005
Variables - declaring
var name
memory loc
main() { float hours; float payrate; float grosspay; int j;
hours = 40.0;
payrate = 20.00;
grosspay = hours * payrate
j = 5;
j = j + 1;
hours
40.0
4278
payrate
20.0
427C
4280
grosspay
800.00 j
5 6
4284
note: referencing a variable only "reads" it (non-destructive). Assigning to a variable overwrites whatever was there (destructive).
(c) 2005, P. H. Viall

12. ECE 160 - Introduction to Computer Engineering I
02/09/2005
scanf() function
Used to get input from user
returns number of items assigned
first argument if format specifiers
remaining arguments are addresses of variables
(c) 2005, P. H. Viall

13. ECE 160 - Introduction to Computer Engineering I
02/09/2005
scanf() function
Documentation info:
int scanf(const char *format [,argument] ...)
format - is format specifiers similar to printf() specifiers
arguments - are ADDRESSES of where to store what the user enters
(c) 2005, P. H. Viall

14. ECE 160 - Introduction to Computer Engineering I
02/09/2005
scanf() function
int hours; float rate;
scanf("%d %f",&hours,&rate);
If user types:
34 5.7
hours ?
1284
rate ?
1288
hours 34
1284
rate
5.7
1288
(c) 2005, P. H. Viall

15. ECE 160 - Introduction to Computer Engineering I
02/09/2005
scanf() function
#include <stdio.h>
int main() { int hours; float rate; float grosspay; printf("Enter hours: "); scanf("%d",&hours); printf("Enter pay rate: "); scanf("%f",&rate); grosspay = hours * rate; printf("You earned $%8.2f\n",grosspay); }
(c) 2005, P. H. Viall

16. scanf() function - Payroll Ver 2
ECE Introduction to Computer Engineering I
02/09/2005
scanf() function - Payroll Ver 2
#include <stdio.h>
int main() { double hours; double rate; double grosspay; printf("Enter hours: "); scanf("%lf",&hours); printf("Enter pay rate: "); scanf("%lf",&rate); grosspay = hours * rate; printf("You earned $%8.2lf\n",grosspay); }
could use %8.2f, but really should use lf
(c) 2005, P. H. Viall