Another important feature of C language is that it may include instructions for the compiler. Though these instructions are not directly the part of C language, they expand the scope of programming environment. These are known as preprocessor. In this chapter, we will discuss about these preprocessors.

A unique feature of C language is the preprocessor. The C preprocessor, as its name implies, processes before the processing of C source program. It is a program that processes the source code before the compiler translates the source code into the object code. During processing, these preprocessors perform some modifications on the source code based on the instructions provided by the preprocessors. These instructions are known as preprocessor commands or directives. Each of the Preprocessor directives begin with a # symbol and do not require semicolon(;) at the end. The preprocessor is used to make the source code more readable, much easy to modify, portable and more efficient.

Some common Preprocessor directives are:

• #define directive – To define a symbolic constant or macro.

• #undef directive – To undefine a symbolic constant or macro.

• #include directive – To include another file in a source program.

• Conditional Compilation directive – To compile parts of source code conditionally.

We already discussed about #define and #include directive in brief. Here they would be discussed in details along with other directives.

Operators are analogous with the verb of English language. It tells what operation has to be performed on operand(s). C language has a rich set of operators. It has 45 different operators. But it does not have any operator to calculate exponent. So, we cannot calculate ab using some operators. For this, C provides a mathematical function named pow( ). In this chapter, we will discuss about most of the operators and their use. An Expression is a combination of variables, constants and operators to produce new values. Expressions are the backbone of C statement which is analogous with the sentence of English language. In this chapter, we will discuss about these building blocks.

OPERATORS IN C

Operators are the symbols that help the programmer to instruct the computer to perform certain arithmetic, relational or logical operation. Operators are used in C language program to operate on data and variables. One of the distinguished features of C language is its rich set of operators. The operators of C can be categorized as:

• 1. Arithmetic operators

• 2. Assignment operators

• 3. Increment and decrement operators

• 4. Relational operators

• 5. Logical operators

• 6. Conditional operators

• 7. Bitwise operators

• 8. Special operators

In addition to this classification operators can also be classified as unary, binary and ternary according to the number of operands associated with the particular operator.

Arithmetic Operators

All the basic arithmetic operations used in mathematics are available in C. These operators bear more or less same meaning in other languages also. C language supports both unary and binary arithmetic operators.

In the last two chapters, we have learnt to develop programs that used simple sequential statements or conditional statements. In the first case, each statement in the program is executed in a fixed order; whereas in the second case, depending on some condition a particular set of statements gets executed, skipped or another set of statements gets executed. But most of the time we have to execute same series of actions. The mechanism, which helps us to perform an action over and over, is the ‘loop’ or ‘iteration’.

Loops are of two types, entry controlled loop and exit controlled loop. When condition is checked before the execution of the body of the loop, it is called entry controlled loop or pre-test iteration. It is described by the following block diagram.

As the block diagram described, first condition will be checked. If the condition is true, the control will enter in the loop and body of the loop will execute. Then control will loop back and the condition will be tested again. This process will be continued until the condition becomes false. When the condition becomes false, control will terminate the loop and execute the next statement followed by the loop statement.

But when condition is checked after the execution of the body of the loop, it is called exit controlled loop or post test iteration. Here, first body of the loop will execute. Then condition will be checked to determine whether the loop will execute next time or not. If the condition is true, the control will loop back. When the condition becomes false, control will terminate the loop and execute the next statement followed by the loop statement. It is described by the following block diagram.

We know that to store a set of elements we need to declare an array. But when we handle large set of elements there are some disadvantages of array. First of all the allocation of an array is static. Thus we need to mention the size of the array before compilation and this size cannot be changed throughout the program. We have to execute the program for fixed specified set of elements. But this is not possible in real life. Suppose, we want to write a program that will read student's name, roll number and marks of various subjects from user or from file and prepare a result sheet in descending order of total marks. If we write this program using an array, then it will be executed for fixed number of students. But generally in different classes or sections number of students varies. So, a single program is not sufficient. We need to write programs for each class/ section; though the program logic is same for all cases. Different program is required only for different array size. One solution is to declare an array which is sufficiently large. But this may lead to the problem of wastage of memory. Again in certain situation, if more elements need to store than the defined one, then it also faces the lack of memory problems. Sometimes it may happen that requirement may changes with the time. In these cases, old programs are needed to modify. Solution of these problems is Dynamic Allocation. But only Dynamic Allocation is not the solution. Sometimes it is not always possible to predict the size of the array at the very beginning of the program.

The basic principle to define a function is to divide a large program into some smaller modules so that a complicated task can be broken into simpler and more manageable form that can be handled easily. These smaller modules are used to accomplish a definite task.

Function is a self-contained block of statements that perform some specific job. In C language, we achieve the modular programming using function. Functions in C are categorized into two groups. They are Library function and User defined function. Library functions are defined within several header files as per individual category of the functions. We already discussed some library functions and some other will be discussed later. Though C supports a large number of library functions, but this is not sufficient. According to our requirement we need to define our own functions. These are called user defined function. In this chapter we will discuss how a user defined function can be defined and how it can be accessed, etc.

Basically, any C program is a collection of one or more functions. If it contains only one function, then it is the main function. In C program main function is a special function. Every C program starts its execution from main function and other functions are called from this function as well. Every C program must have a main function and more than one main function is not possible in a single program. However, a C program may contain more than one user defined function and there is no restriction on this.m

Answer to Model Question Set-4

In the last chapter, we discussed about single and multi dimensional array. We already learnt how to define arrays of different sizes and dimensions, how to initialize them, how to operate on arrays of different dimensions, etc. With this knowledge, we are ready to handle strings, which are, simply a special kind of array. String handling basically consists of:

Σ Input and output strings from/to keyboard/monitor or files.

Σ Copying and comparing strings with library functions.

Σ Finding substrings, determining length, extracting substring, concatenating strings with library functions.

Σ Manipulating case of characters in a string with library functions.

Σ Writing equivalent functions of string manipulating library functions.

We will discuss all important string manipulating library functions in this chapter; however a complete list of string manipulating library functions along with explanation is given in Appendix.

We will learn to write equivalent functions of string manipulating library functions in functions chapter.

STRING

A string is a sequence of characters terminated with a null character (‘\0’). It is usually stored as one-dimensional character array. A set of characters arranged in any sequence defined within double quotation is known as string constant. To manipulate text such as words and sentences, strings, i.e., character arrays are used. The way a group of integers can be stored in an integer array, is similar with a group of characters stored in a character array.