CHAPTER 2:Getting Started with C

Introduction

Computer is a machine that can perform computation

Input:User gives a set of Input
Processing:Input data is processed by a well defined and finite sequence of steps
Output:Some data available from processing step and output to the user

A Computer (Level 0 Version) — Figure 2.0:

Programming and Software

Computer needs to be programmed to do such tasks:-

Programming: is the process of writing instructions in a language that can be understood by the computer so that a desired task can be performed by it
Program: sequence of instructions to do a task,computer processes the instructions sequentially one after the other
Software: programs for doing tasks on computers

Structure Of C Program

A collection of functions (we will see what they are later)
Exactly one special function named main must be present.Program always starts from there
Each function has statements (instructions) for declaration, assignment, condition check,looping etc.
Statements are executed one by one.

Variables

Very important concept for programming.
Variables stored in memory.
An entity that has a value and is known to the program by a name.
It Can store any temporary result while executing a program.
It Can have only one value assigned to it at any given time during the execution of the program.
The value of a variable can be changed during the execution of the program.
Remember that memory is a list of storage locations,each having a unique address.
A variable is like a bin:-

The contents of the bin is the value of the variable.
The variable name is used to refer to the value of the variable.
A variable is mapped to a location of the memory,called its address.

Variables in Memory

How to give Names of Variable

Sequence of letters and digits
First character must be a letter or _
No special characters other than _
No blank in between
Names are case-sensitive (max and Max are two different names)

Examples of valid names:

rank1, MAX, max, Min, class_rank

Examples of invalid names:

's ,fact rec,2sqroot,class?rank

Constants

Integer constants

Consists of a sequence of digits, with possibly a plus or a minus sign before it
Embedded spaces, commas and non-digit charactersare not permitted between digits

Floating point constants
Two different notations:

Decimal notation: 25.0, 0.0034, .84, -2.234
Exponential (scientific) notation 3.45e23, 0.123e-12, 123e2 e means 10 to the power of

Character constants
Contains a single character enclosed within a pair of single quote marks.

Examples :' 2 ', ' + ' , ' Z '

Some special backslash characters

'\n'	new line
'\t'	horizontal tab
'\' '	single quote
'"'	double quote
'\\'	backslash
'\0'	null

        Illustration 2.3
        #include<stdio.h >
        void main()
        {
          int x;
          int y;
          x=1;
          y=3;
          printf("x = %d, y= %d\n", x, y);
        }

        Output:
        x=1, y=3

C Keywords

Used by the C language, cannot be used as variable names
Examples:

int, float, char, double, main, if else, for, while,do, struct, union, typedef, enum, void, return,signed, unsigned, case, break, sizeof etc.
There are others, see textbook.

Input:Scanf function

Performs input from keyboard
It requires a format string and a list of variables into which the value received from the keyboard will be stored
format string = individual groups of characters(usually '%' sign, followed by a conversion character),with one character group for each variable in the list

                int a, b;
                float c;
                scanf(%d %d %f, &a, &b, &c);

Commonly used conversion characters

c :for char type variable
d :for int type variable
f :for float type variable
lf :for double type variable

Examples:
scanf("%d", &size) ;
scanf("%c", nextchar) ;
scanf("%f", &length) ;
scanf("%d%d", &a, &b);

Reading a single character

A single character can be read using scanf with %c
It can also be read using the getchar() function
Program waits at the getchar() line until a character is typed, and then reads it and stores it in c

char c;
c = getchar();

Data types

Each variable has a type, indicates what type of values the variable can hold

Four common data types in C:

int - can store integers (usually 4 bytes)
float - can store single-precision floating point numbers (usually 4 bytes)
double - can store double-precision floating point numbers (usually 8 bytes)
char- can store a character (1 byte)

Must declare a variable (specify its type and name) before using it anywhere in your program
All variable declarations should be at the beginning of the main() or other functions
A value can also be assigned to a variable at the time the variable is declared.