Displaying variables-
The function
printf is used to display output on the standard output devices.
/* An example illustrating
an integer output */
#include<stdio.h>
void main()
{
int num;
num=10;
printf (“%d”, num);
}
The first line
in the program starts with /* and ends with */. Any thing written between /*
and */ is called comment. In the C language, comments are an aid to the
programmer to read and understand the program. It is not the statement of the
language. The compiler ignores the comments.
The second
line i.e. #include<stdio.h>
This is called
the preprocessor directive. It is usually written in the beginning of the
program. It commands that the contents of the file stdio.h should be included
in the compiled machine code at the place where #include appears. The file
stdio.h contains the standard input output routines.
The next line
is main (). It is a function in C. The main () function is required in all C
programs. The execution of program starts from the main (). It is like the main
() entry gate for the execution of the program. Note that main () is not
followed by a comma or semicolon.
The next line
is opening brace { . All the C statements must be enclosed within opening brace
and closing brace.
In C, all the
variables must be declared before using them. The next line in the program is
int num;
The statement
is called declaration of the integer type of variable. It informs compiler that
num is a variable name and a memory location must be reserved for it in memory.
In fact, this statement allocates one memory location named num.
The next
statement num=10; assigns integer value 10 to the memory location num having
certain address.
The next
statement is printf(“%d”, num);.
This is an
output function or output statement in C, It displays the content of memory
location num at the standard output device VDU. The %d following the left
parentheses is known as the conversion specification. Its role is to specify
that the number is to be converted to decimal notation before being printed.
Observe, every
statement is terminated by semicolon (;). When C compiler comes across with
this terminator, it will come to know that it is the end of the statement.
The general
form of printf statement is
printf(“conversion
specifier”, List of variables);
Format string
could be:
%f for
printing real variables
%d for
printing integer values
%c for
printing character values
Note: main ()
is the only function with return 0, at the end. When control crosses the
ending} of main (), it returns control to the operating system by returning 0
to it. The OS normally treats return 0 as the successful termination of the
program. Some compiler may accept void main () or any other return type.
/* An example
illustrating integer and floating output */
#include<stdio.h>
void main ()
{
int num1;
float num2;
num1=10;
num2=35.32;
printf(“num1 is %d and num2
is %f”,num1, num2);
}
Output:
num1 is 10 and num2 is 35.32
Two variables,
namely num1 of type int and num2 of type float are declared. These statements
create two memory locations of type int and float.
The next two
statements sum1=10 and num2=35.32 assign 10 to the integer type of memory
location num1 and 35.32 to float type.
Inside printf
statement, the format %d and %f specify the type of variables to be output. They
are called conversion specifier. To first conversion specifier, %d corresponds
to the first parameter num1. It informs printf that num1 is an integer type of
data. Similarly, the second conversion specifier, %f corresponds to the second
parameter num2 and informs printf that num2 is a float type of data.
printf(“num1
is %d and num2 is %f”,num1,num2);
%d is replaced
by the value of the parameter num1 and %f by the value num2.
The scanf()
function reads the values of variables from the standard device(keyboard) and
stores them in variables. The example below reads the two values from the
keyboard and displays it on the standard output device.
/* an example illustrating
reading of variables */
#include<stdio.h>
void main()
{
int num1,num2;
printf(“Enter the two
number”);
scanf(“%d%d”,&num1,&num2);
printf(“The numbers are %d
and %d”, num1,num2);
}
Output:
Enter the two numbers
24 45
The numbers are 24 and 45
After the
execution of the statement int num1, num2; two memory location namely num1 and
num2 of type integer are allocated.
The statement
printf (“Enter the two numbers”); displays string on the monitor.
scanf (“%d
%d”, &num1, &num2);
The scanf
function stores the input value in memory. To perform this, it must know the
name and address of the variable in memory.
The first
conversion specifier %d corresponds to num1 preceded by an ampersand and second
%d corresponds to num2 preceded by an ampersand for storing integer type of
data. Here ampersand is address operator which is used for sending address of
variables num1 and num2 to scanf ().
Again the
statement printf (“….”) displays the content of memory at the standard output
device.
Certain ASCII
characters are unprintable which means they are not displayed on the screen.
Some of the more commonly used escape sequences.
Escape Sequence Meaning
\a alert
(bell)
\f form
feed
\b back
space
\n new
line
\r carriage
return
\t horizontal
tab
\v vertical
tab
\\ backslash
\? Question
mark
\’ single
quote
\” double
quote
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