ques: What do you mean by tupe conversion?
Ans: In an expression there mllight be cases when you need to involve different types of variable in a single expression. For example an expression may contain addition of two integers and the result is requird to be multiplied by a float. The expressions that contain variables and constants are evaluated using the following methods known as type conversions. These data types are required to be converted for easy calculation of the exprssion. These conversions are implicity done be the system.
4 comments:
ques: What do you mean by Local variable or global variable?
Ans: Local variables are defined with in a pair of braces r between the body of the function . The scope of the variable is with in the function when function finished they will be obsolete.
2.Global variables defined outside all the funtion. And can be used to any function with in file because the scope of these variable are global to the file.
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Arrays and Strings
In principle arrays in C are similar to those found in other languages. As we shall shortly see arrays are defined slightly differently and there are many subtle differences due the close link between array and pointers. We will look more closely at the link between pointer and arrays later in Chapter 9.
Single and Multi-dimensional Arrays
Let us first look at how we define arrays in C:
int listofnumbers[50];
BEWARE: In C Array subscripts start at 0 and end one less than the array size. For example, in the above case valid subscripts range from 0 to 49. This is a BIG difference between C and other languages and does require a bit of practice to get in the right frame of mind.
Elements can be accessed in the following ways:-
thirdnumber=listofnumbers[2];
listofnumbers[5]=100;
Multi-dimensional arrays can be defined as follows:
int tableofnumbers[50][50];
for two dimensions.
For further dimensions simply add more [ ]:
int bigD[50][50][40][30]......[50];
Elements can be accessed in the following ways:
anumber=tableofnumbers[2][3];
tableofnumbers[25][16]=100;
Strings
In C Strings are defined as arrays of characters. For example, the following defines a string of 50 characters:
char name[50];
C has no string handling facilities built in and so the following are all illegal:
char firstname[50],lastname[50],fullname[100];
firstname= "Arnold"; /* Illegal */
lastname= "Schwarznegger"; /* Illegal */
fullname= "Mr"+firstname
+lastname; /* Illegal */
However, there is a special library of string handling routines which we will come across later.
To print a string we use printf with a special %s control character:
printf(``%s'',name);
NOTE: We just need to give the name of the string.
In order to allow variable length strings the 0 character is used to indicate the end of a string.
So we if we have a string, char NAME[50]; and we store the ``DAVE'' in it its contents will look like:
Exercises
Exercise 12335
Write a C program to read through an array of any type. Write a C program to scan through this array to find a particular value.
Exercise 12336
Read ordinary text a character at a time from the program's standard input, and print it with each line reversed from left to right. Read until you encounter end-of-data (see below).
You may wish to test the program by typing
prog5rev | prog5rev
to see if an exact copy of the original input is recreated.
To read characters to end of data, use a loop such as either
char ch;
while( ch = getchar(), ch >= 0 ) /* ch < 0 indicates end-of-data */
or
char ch;
while( scanf( "%c", &ch ) == 1 ) /* one character read */
Exercise 12337
Write a program to read English text to end-of-data (type control-D to indicate end of data at a terminal, see below for detecting it), and print a count of word lengths, i.e. the total number of words of length 1 which occurred, the number of length 2, and so on.
Define a word to be a sequence of alphabetic characters. You should allow for word lengths up to 25 letters.
Typical output should be like this:
length 1 : 10 occurrences
length 2 : 19 occurrences
length 3 : 127 occurrences
length 4 : 0 occurrences
length 5 : 18 occurrences
....
To read characters to end of data see above question.
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BASIC OF C LANGUAGE
ANS:
C Basics
Before we embark on a brief tour of C's basic syntax and structure we offer a brief history of C and consider the characteristics of the C language.
In the remainder of the Chapter we will look at the basic aspects of C programs such as C program structure, the declaration of variables, data types and operators. We will assume knowledge of a high level language, such as PASCAL.
It is our intention to provide a quick guide through similar C principles to most high level languages. Here the syntax may be slightly different but the concepts exactly the same.
C does have a few surprises:
Many High level languages, like PASCAL, are highly disciplined and structured.
However beware -- C is much more flexible and free-wheeling. This freedom gives C much more power that experienced users can employ. The above example below (mystery.c) illustrates how bad things could really get.
History of C
The milestones in C's development as a language are listed below:
UNIX developed c. 1969 -- DEC PDP-7 Assembly Language
BCPL -- a user friendly OS providing powerful development tools developed from BCPL. Assembler tedious long and error prone.
A new language ``B'' a second attempt. c. 1970.
A totally new language ``C'' a successor to ``B''. c. 1971
By 1973 UNIX OS almost totally written in ``C''.
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