IPC144
Session 11
The C Programming Language
1
Objectives
To format a #define statement correctly
To use a #define statement in a C program
To construct a printf() statement
To use a printf() statement in a C program
To construct a scanf() statement
To use a scanf() statement in a C program

2
The C Language
Introduction
What can you tell me about the following C statement?
#define
3
The C Language
Introduction
What can you tell me about the following C statement?
#define
It is a preprocessor directive
4
The C Language
#define
What value is the #define preprocessor directive?
Remember the Library Fines Calculator program- the fine was set to $0.05
There was one place in the program where we used the fine. What if there were many
places in the program?
Imagine if the fine was $0.07, and the Library had to charge PST of $0.07? Perhaps the
fine need to be increased to $0.10. You would be looking at many lines of code trying to
determine if the 0.07 related to the fine or the tax.
5
The C Language
#define, continued
A sensible way to code your program would be to 'define' names that will represent the
value throughout the program.
THESE ARE NOT VARIABLES- when the preprocessor processes the source code- the
names are replaced the value before being passed on to the translator.
For example we could create a name called PST_TAX and another name FINE to
represent the values that need to be used in the Library program. We can use these
names in place of the 0.07 value, and be able to differentiate between which 0.07 relates to
tax and which 0.07 relates to the fine.
In C this looks like:
#define PST_TAX 0.07
#define FINE
0.07
...
totalFine = (overDue * FINE) + ((overDue * FINE) * PST_TAX);
6
The C Language
#define, continued
Anatomy of the #define statement:
#define name value
NOTE: there is no semicolon at the end
This is the value the name represents
This is the name that will be used throughout the program
This is the 'define' preprocessor directive
As discussed already, this indicates as preprocessor directive
7
The C Language
#define, continued
How the #define works:
The preprocessor creates a list of the names and their values

The preprocessor then searches through the program looking for the name

When the preprocessor finds the name, it is replaced with the corresponding value

The value is considered to start on the first non-blank character after the name, and ends
at the last non-blank character before the end of the line or comment.

#define MYDEFINE
32134325235 35
start
end
8
The C Language
#define, continued
Coding Standard:
When creating a #define, the name must be in uppercase letters. The underscore
character is used to separate the words of a compound name
The #define statements follow the #include statements in your source file
All quantities that remain unchanged throughout a program must be named using the
#define
9
The C Language
#define, continued
The only time that the changes made to a #define is reflected in your program is after you
recompile the program.
10
The C Language
printf() function
This is the equivalent of the DISPLAY statement in pseudocode.
Whatever formatted data is output by the printf() statement is sent to the standard output
device of the computer - in our case the monitor.
11
The C Language
printf() function, continued
Anatomy of a simple printf() statement:
printf("A program is born.\n");
An "escape sequence" that is used to tell the
computer you want to go to a NEWLINE
The beginning of a string of data to be printed EXACTLY as written
The library function being called
NOTE where the opening and closing brackets are, and what is placed inside of the
double quotes.
12
The C Language
printf() function, continued
Example:
#include <stdio.h>
int main(void)
{
printf("A program is born.\n");
printf("\nOh, sure you think it's cute and cuddly now\n");
printf("but just wait!\nAs it grows up it will become a ");
printf("monster before you know it!\n");
}
What is the output of this program?
13
The C Language
printf() function, continued
#include <stdio.h>
int main(void)
{
printf("A program is born.\n");
printf("\nOh, sure you think it's cute and cuddly now\n");
printf("but just wait!\nAs it grows up it will become a ");
printf("monster before you know it!\n");
}
A program is born.
Oh, sure you think it's cute and cuddly now
but just wait!
As it grows up it will become a monster before you know it!
14
The C Language
printf() function, continued
We have defined variables in our C program, how do we display their contents?
There are two parts to the printf() function:
The format string, which contains:
literal text to be output exactly as written
special control characters (such as the \n)
field specifications
A list of variables that correspond the field specifications in the format string

The format string is like a template, showing you where the text is (and what the text
is) as well as where within the text the values of the variables are to be inserted
15
The C Language
printf() function, continued
example:
printf("Total = %d
Average = %f\n", ttl, avg);
The field specifications are "place holders" for the variable data that the program is
calculating
Where-ever you place a field specification, the compiler will look for a corresponding
variable in the list of variables
The first field specification refers to the first variable in the list, the second field
specification refers the second variable in the list and so on...
16
The C Language
printf() function, continued
The field specifications in the format string that correspond to the data types
discussed:
%c
-
char
%d
-
int
%f
-
float
%hd
-
short int
%ld
-
long int
%Lf
-
long double
17
The C Language
printf() function, continued
The field specification format is:
%
flags
minimum width
.precision
size
conversion code
Flags provide extra control over the formatting of numbers, and to indicate leftjustify. By default the flags are not set.
- left justify the field
+ print positive numbers with a leading '+' sign
(there is a space at the beginning of this line). Print positive numbers with leading
spaces
18
The C Language
printf() function, continued
The field specification format is:
%
flags
minimum width
.precision
size
conversion code
Minimum width of the print zone by default is the total width of the value including
any characters added by the use of the flags and precision.
If the total width of the value is less than the specified width, then the value is rightjustified within the print zone. If the '-' flag is used, the value is left-justified.
If the total width of the value is greater than the minimum width, the print zone will
be extended to accommodate the value. The value is not truncated.
If set to '*', the width field can be based on an integer value found in the variable list
int i = 5, j = 4;
printf(“%*d\n”, j, i);
printf(“%4d\n”, i);
is the same as:
19
The C Language
printf() function, continued
The field specification format is:
%
flags
minimum width
.precision
size
conversion code
Precision has different effects depending on the data type of the variable being
printed
Integers -
minimum numbers of digits to print. Pad with leading zeroes if
necessary
Float
maximum number of digits to print on the right side of the decimal
point (default is six digits).
-
If set to '*', the precision field can be based on an integer value found in the variable
list
int i = 5, j = 4, k = 3;
printf(“%*.*d\n”, j, k, i);
printf(“%4.3d\n”, i);
is the same as:
20
The C Language
printf() function, continued
The field specification format is:
%
flags
minimum width
.precision
size
conversion code
Size modifies the data type represented by the conversion code:
h
-
Use with 'd' to specify short int
l
-
used with 'd' to specify a long int
L
-
used with 'f' to specify a long double
21
The C Language
printf() function, continued
The field specification format is:
%
flags
minimum width
.precision
size
conversion code
Conversion code specifies the data type, and in most cases the format, and in some
cases the format in which it is to be printed:
d -
int, signed decimal number, no fractions
f -
float, signed decimal number with 6 decimal numbers (rounding takes place)
%-
so that you can print a '%' character
22
The C Language
printf() function, continued
What is the printf() format string to produce the required output given the data type
and the value of the variable myVar:
Data Type
int
float
int
float
Value
1
1.345
56
2.1
Required output
001
+1.35
56
2.10%
The 'required output' field is 15 characters in size.
23
The C Language
printf() function, continued
What is the printf() format string to produce the required output given the data type
and the value of the variable myVar:
Data Type
int
float
int
float
Value
1
1.345
56
2.1
Required output
001
+1.34
56
2.10%
"%15.3d"
"%+15.2f“
"%-15d“
"%-15.2f%%"
The 'required output' field is 15 characters in size.
24
The C Language
scanf() function
A computer program is fairly limited if it cannot get input data from a user as it is
executing
There exists a function that is very similar to the printf() function that is used for
formatted input
Anatomy of the scanf() statement:
scanf("format string", v1, v2, ...);
A list of variables that are referenced in the
format string. Each variable of type char, int or float is preceded by
a '&' character
A list of field specifications for the data being read
The function being called
25
The C Language
scanf() function, continued
There is one major difference with the scanf() function when dealing with the
variables:
scanf("%d", &i);
Notice the "&" symbol before the variable name
This is called the "address-of" operator
For now, it means that when you place the value read from the user into the variable,
you can only store the data if you know the address of the variable within the
computer's memory
26
The C Language
scanf() function, continued
The field specification format is:
%
flags
maximum width
size
conversion code
Flag in this case is called assignment suppression character. It has only one value:
*
This indicates the input is to be discarded
Its purpose is to be able to skip over a sequence of characters in the input file.
Input file in this case, by definition, includes the keyboard.
27
The C Language
scanf() function, continued
The field specification format is:
%
flags
maximum width
size
conversion code
Maximum width indicates the maximum characters to be read into the variable.
Scanning for integers and floats, stops when a white-space character is found, an
invalid character is found (strictly based on the data type), or the scan has hit the end
of the file.
28
The C Language
scanf() function, continued
The field specification format is:
%
flags
maximum width
size
conversion code
Size behaves the same way as in the printf() function.
29
The C Language
scanf() function, continued
The field specification format is:
%
flags
maximum width
size
conversion code
The conversion code also behaves the same way as in the printf() function.
30
The C Language
scanf() function, continued
Exercise:
What would be the values of the variables if the scanf() function were to be executed
within the data types specified and the input data specified:
Data Type
int i;
Input Data scanf() function
12334
scanf("%d", &i);
Variables after Read
i =
int i;
float x;
155.347 7 scanf("%d %f", &i, &x); i =
x =
int i1;
int i2;
1234
scanf("%3d%d", &i1, &i2); i1 =
i2 =
31
The C Language
scanf() function, continued
Exercise:
What would be the values of the variables if the scanf() function were to be executed
within the data types specified and the input data specified:
Data Type
int i;
Input Data scanf() function
12334
scanf("%d", &i);
Variables after Read
i = 12334
int i;
float x;
155.347 7 scanf("%d %f", &i, &x); i = 155
x = 0.347
int i1;
int i2;
1234
scanf("%3d%d", &i1, &i2); i1 = 123
i2 = 4
32