c-introduction-c.sc dept, nit, raichur

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Objectives

Structure of a C-language program.

First C program.

Preprocessors.

Identifiers for objects in a program.

C basic Data Types.

Usage of Variables and Constants.

Input and Output concepts.

I ntroduction to the C Language

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C History

Developed between 1969 and 1973 alongwith Unix

Due mostly to Dennis Ritchie

Designed for systems programming

Operating systems

Utility programs Compilers

Filters

Evolved from B, which evolved from BCPL

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Background

C is a structured programming language. I t is

considered a high-level language because it allows the

programmer to concentrate on the problem at hand

and not worry about the machine that the program

will be using. While many languages claim to be

machine independent, C is one of the closest to

achieving that goal. That is another reason why it is

used by software developers whose applications have

to run on many different hardware platforms.

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C History

Original machine (DECPDP-11) was very small

24K bytes of memory, 12Kused for operating system

Written when computerswere big, capital

equipment Group would get one,

develop new language, OS

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Taxonomy of the C Language

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C Programs

I t' s time to wr ite your f irst C program! This section

will take you through all the basic parts of a C

program so that you wil l be able to write it.

Structure of a C ProgramYour First C Program

Comments

The Greeting Program

Topics discussed here :

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Structure of a C Program

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The Greeting Program

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Examples of Block Comments

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Examples of Line Comments

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Nested Block Comments Are Invalid

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Computer Science: A Structured Programming Approach Using C 12

PROGRAM 2-1 The Greeting Program

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2-3 Identifiers

One feature present in al l computer languages is the

identi f ier. I denti f iers allow us to name data and other

objects in the program. Each identi f ied object in the

computer is stored at a unique address. I f we didn’t  have identifiers that we could use to symbolically

represent data locations, we would have to know and

use object’s addresses. I nstead, we simply give data

identi f iers and let the compiler keep track of where

they are physical ly located.

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Table 2-1 Rules for Identifiers

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An identifier must start with a letter or underscore:

it may not have a space or a hyphen.

Note

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C is a case-sensitive language.

Note

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C Type Examplesint i;

int *j, k;

unsigned char *ch;

float f[10];

char nextChar(int, char*);

int a[3][5][10];

int *func1(float);

int (*func2)(void);

Integer

 j: pointer to integer, int k

ch: pointer to unsigned char

Array of 10 floats

2-Arguments function

Array of three arrays of five … 

function returning int *

pointer to function returning int

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C Expression Classes arithmetic: + – * / % comparison: == != < <= > >= bitwise logical: & | ^ ~ shifting: << >>

lazy logical: && || ! conditional: ? : assignment: = += -=

increment/decrement: ++ -- sequencing: , pointer: * -> & []

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Examples of Valid and Invalid Names

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Data Types

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Character Types

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Integer Types

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sizeof (short) ≤ sizeof (int) ≤ sizeof (long) ≤ sizeof (long long) 

Note

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Typical Integer Sizes and Values for Signed Integers

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Floating-point Types

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sizeof (float) ≤ sizeof (double) ≤ sizeof (long double) 

Note

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Type Summary

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Variables

Variables are named memory locations that have a type,

such as integer or character, which is inher ited from

their type. The type determines the values that a var iable

may contain and the operations that may be used withits values.

Variable Declaration

Variable Initialization

Topics discussed in this section:

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Variables

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Examples of Variable Declarations and Definitions

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Variable Initialization

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When a variable is defined, it is not initialized.

We must initialize any variable requiring

prescribed data when the function starts.

Note

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PROGRAM 2 Print Sum of Three Numbers

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PROGRAM 2 Print Sum of Three Numbers (continued)

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PROGRAM 2 Print Sum of Three Numbers (continued)

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Constants

Constants are data values that cannot be changed

during the execution of a program. Like variables,

constants have a type. I n this section, we discuss

Boolean, character, integer, real, complex, and str ingconstants.

Constant Representation

Coding Constants

Topics discussed in this section:

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A character constant is enclosed in single quotes.

Note

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Symbolic Names for Control Characters

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Examples of Real Constants

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The two components of a complex constant must be of the

same precision, that is, if the real part is type double,then the imaginary part must also be type double.

Note

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Examples of Complex Constants

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Some Strings

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Use single quotes for character constants.

Use double quotes for string constants.

Note

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PROGRAM 3 Memory Constants

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PROGRAM 3 Memory Constants (continued)