This lesson will teach you how to:
- Initialize variables
- Use arithmetic operators
Q. What's the difference between a lawyer and a gigolo?
A. A gigolo only screws one person at a time.
Initializing data variables at declaration time
Unlike PASCAL, in C variables may
be initialized with a value when they are declared. Consider
the following declaration, which declares an integer variable
count which is initialized to 10:
int count = 10;
Simple assignment of values to variables
The = operator is used to assign values to data variables.
Consider the following statement, which assigns the value
32 an integer variable count, and the letter A
to the character variable letter :
count = 32;
letter = ‘A’;
The value of variables at declaration time
Lets examine what the default value a variable is assigned
when its declared. To do this, lets consider the following
program, which declares two variables, count which is an
integer, and letter which is a character. Neither
variable is pre-initialized. The value of each variable
is printed out using a printf() statement.
#include <stdio.h>
int main(void)
{
int count;
char letter;
printf(“Count = %d\n”,
count);
printf(“Letter = %c\n”,
letter);
return 0;
}
Sample program output
count = 26494
letter = f
It can be seen from the sample output that the values which
each of the variables take on declaration time are non-zero.
In C, this is common, and programmers must ensure that variables
are assigned values before using them. If the program runs
again, the output could well have different values for each
of the variables. We can never assume that variables declare
in the manner above will take on specific values. Some compilers
may issue warnings related to the use of variables, and
Turbo C from Borland issues the following warning:
“possible use of ‘count’
before definition in function main”
Radix changing
Data umbers may be expressed in any base by simply altering
the modifier, e.g. decimal, octal, or hexadecimal. This
is achieved by the letter which follows the % sign related
to the printf() argument.
#include <stdio.h>
int main(void) /*
Prints the same value in decimal, hex, and octal */
{
int number = 100;
printf(“In decimal the
number is %d\n”, number);
printf(“In hex the number
is %x\n”, number);
printf(“In octal the number
is %o\n”, number);
/*
what about %X as an argument? */
return 0;
}
Sample program output
In decimal the number is 100
In hex the number is 64
In octal the number is 144
Note how the variable number is initialized to one hundred
at the time of its declaration.
Defining variables in octal and hexadecimal
Often, when writing systems programs, the programmer needs
to use a different number base rather than the default decimal.
Integer constants can be defined in octal or hex by using
the associated prefix, e.g. to define an integer as an octal
constant use %o
int sum = %o567;
To define an integer as a hex constant use %Ox
int sum = %Ox7ab4;
int flag = %Ox7AB4;
/*
Notice upper or lower case are not the same variables
*/
Arithmetic Operators:
The symbols of the arithmetic operators are:
If a line has an expression which contains several operators
of equal priority, C will evaluate if from left to right.
Note that in C, the equal (=) sign is a replacement operator.
This means that the expressions such as a = b = c are permissible,
but order of evaluation is now from right to left, so that
c would be assigned to b, which in turn would be assigned
to a, giving all three variables the same value, namely
that of c.
The following code fragment adds the variables loop and
count together, leaving in the variable sum:
sum = loop + count;
Note: If modulus % sign is needed to be displayed as part
of the text string, use two % signs, e.g. %%.
#include <stdio.h>
int main(void)
{
int sum = 50;
flat modulus;
modulus = sum % 10;
printf(“The %% of %d by
10 is %f\n”, sum, modulus);
return 0;
}
Sample program output
The % of 50 by 10 is 0.000000
back to top exercises lesson
3 lesson
5
