1. Engr 0012 (04-1) LecNotes 19-01

2. Variable (data object) declaration in C
variable attributes
address (where located in computer)
C assigns this
type of information
programmer assigns this
value
user or programmer assigns this
Engr 0012 (04-1) LecNotes 19-02

3. Variable (data object) declaration in C
types of variables
Engr 0012 (04-1) LecNotes 19-03

4. 154 Variable (data object) declaration in C 0065FDF4
two methods of variable declaration
Value-oriented
int a;
Address-oriented
int *pa;
address
154 a
int
0065FDF4
address
0065FDF4 pa
int
address
0065FE4D
name
name
type
type
a ==> value (154)
pa ==> address (0065FDF4)
&pa ==> address (0065FE4D)
&a ==> address
(0065FDF4)
*pa ==> value (154)
Engr 0012 (04-1) LecNotes 19-04

5. Variable (data object) declaration in C
value-oriented declarations
int myfunction( int i1, double d1 )
// myfunction description
{ //begin myfunction
// variable declaration
int i2,i3; // two ints
double d2,d3; // two doubles
char c1; // a character
// algorithm …
} //end myfunction
seen in prototype parameter list
seen in variable declaration section
most common declaration - emphasizes value
Engr 0012 (04-1) LecNotes 19-05

6. Variable (data object) declaration in C
value-oriented declarations
int myfunction( int i1, double d1 )
// myfunction description
{ //begin myfunction
// variable declaration
int i2,i3; // two ints
double d2,d3; // two doubles
char c1; // a character
// algorithm …
} //end myfunction
sets up memory map on scrap paper
&i1 &d1 &i2 &i3 &d2 &d3 &c1_
?? ?? ?? ?? ??
where did these values come from?
Engr 0012 (04-1) LecNotes 19-06

7. Variable (data object) declaration in C
address-oriented declarations
void myfnc2( int i1, int *pi2, int *pi3 )
// myfnc2 description
{ //begin myfunction
// variable declaration
int i4,i5; // two ints
double d1,d2; // two doubles
char c1; // a character
// algorithm …
} //end myfunction
seen in prototype parameter list
used when we want to share an address between functions
Engr 0012 (04-1) LecNotes 19-07

8. Variable (data object) declaration in C
address-oriented declarations
void myfnc2( int i1, int *pi2, int *pi3 )
// myfnc2 description
{ //begin myfunction
// variable declaration
int i4; // an int
double d1; // a double
char c1; // a character
// algorithm …
} //end myfunction
sets up memory map on scrap paper
&i1 &pi2 &pi3 &i4 &d1 &c1_
4 62AE 62AF ?? ?? ??
contents are addresses!
where do these come from?
Engr 0012 (04-1) LecNotes 19-08

9. function prototypes/calling statements
value-oriented parameters require values
address-oriented parameters require addresses
double fcn1( int i1, double d1, int *pi2 )
possible calling statements
a = fcn1( 1, 3.2, &myint );
q = fcn1( alpha, beta, &thisint );
w = fcn1( alpha, cos(beta), &anyint );
Engr 0012 (04-1) LecNotes 19-09

10. getting information from keyboard: scanf
scanf requires two things
type of value expected - denoted by placeholder
where to store value - address of variable
need to
printf
before
scanf
printf( “\nPlease enter an integer ==> ”);
scanf( “%d”, &i1 );
printf( “\nPlease enter a real number ==> ”);
scanf( “%lf”, &d1 );
caution - always flush keyboard buffer before & after char input
printf( “\nPlease enter a character ==> ”);
fflush( stdin );
scanf( “%c”, &c1 );
Engr 0012 (04-1) LecNotes 19-10

11. displaying information to screen: printf
printf requires a control string that tells what to display
values to display are optional!!!
printf( “\nPlease enter an integer ==> ”);
to display values, insert placeholders in control string
& list values (in order) after control string
printf( “\nCircle of radius %.4lf has area %.4lf”,
1, );
printf( “\nCircle of radius %.4lf has area %.4lf”,
radius, circ_area );
Engr 0012 (04-1) LecNotes 19-11

12. placeholders scanf simply enclose placeholder “%d” in double quotes
printf
can format output display
%wd
w is a number that tells how many spaces to use
%w.plf
w tells how many (total) spaces to use
p tells how many decimal places to use
%w.ple
le: (long) scientific notation display
Engr 0012 (04-1) LecNotes 19-12

13. general notes on C
C ignores whitespace - semicolons terminate statements
a = 6.3;
is the same as
a=6.3;
is the same as a =
6.3;
printf( “\nCircle of radius %.4lf has area %.4lf”,
radius, circ_area );
to break a control string for easy reading in the text editor
no comma!
printf( “\nCircle of radius ”
“%.4lf has area %.4lf”,
radius, circ_area );
Engr 0012 (04-1) LecNotes 19-13