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Brief History

C evolved from two previous languages, BCPL and B.
BCPL was developed in 1967 by Martin Richards.
B, in 1970 by Ken Thompson.
Both BCPL and B were “typeless” languages.
C, in 1972 by Dennis Ritchie at Bell Labs.
C is widely used with UNIX operating system.

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History …

Many versions of the language C was created by many people.
This created problems with portability.
In 1999, ANSI (American National Standards Committee) standardized the language and is called ANSI-C.

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C program

C program is a set of functions.
Every C program should have a function with name main( )
Execution of the program starts with main( )
Some functions to do common tasks comes along with the C language. These functions are kept in libraries.

For e.g. the functions to do input and output are in the library called stdio.h

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C Standard Library

Libraries that comes along with C are called standard libraries.
So, you need to learn C language and also how to use the standard libraries.

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A Simple C Program

/* This program Prints Hello word */

#include <stdio.h>

main()

{

printf(“Hello.\n”);

} /* End of main */

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/* This program finds the area & perimeter

of a rectangle */

#include <stdio.h>

main()

{

int l, b, area, perimeter;

b = 4;

l = 6;

area = l*b;

perimeter = 2*(l+b);

printf(“Area = %d \n”, area);

printf (“Perimeter = %d \n”, perimeter);

} /* End of main */

test.c

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Complier ignores comments
#include line must not end with semicolon
Every statement is terminated by semicolon

Output of the program

Area = 24

Perimeter = 20

cc test.c compile program test.c

a.out execute the program

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Variables and Constants

Basic data objects manipulated in a program.
Variable should have a name (identifier) and a value.
Names are made up of letters and digits; the first character must be a letter.
E.g.: total, n, sum1, sum2
“_” (underscore) is also a letter.
E.g.: val_1 is a valid name.
But don’t begin variable names with underscore, since library functions often uses such names.

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Names (Identifiers) …

Upper case and lower case letters are distinct. That is x and X are two different letters.
There are reserve words in the C language, like if, else, int, float, etc., which should not be used as variable names.

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Names …

Invalid names :

$total
1st
no.
case

Are the following valid?

_total
end

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Constants

A data item whose value does not change.
Constants also can have names following the same rules as that for variable names.
Simple numbers like 123, 0.24 are of course constants (which are without name).

More about constants follows later …

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Data Types

There are various categories of data items, like integers, real numbers, character strings, etc.
Each category is called a type.
There are inbuilt types (basic types) and user defined types.

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Basic data types

character (char) 🡺 single character

integer (int) 🡺 an integer number

real (float) 🡺 a real valued number

(double) 🡺 a real valued number with higher precision.

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Declarations

An identifier which you want to use should be declared first.
A declaration specifies type and identifiers name.
Optionally a declaration for a variable can contain its initial value also.

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Declarations …

int count; /* declares that count is a variable which can hold integer values */
char s, c; /* s and c are variables which can hold a single character each */
float sum_1 = 0.5;
double d, total, sum;

Declaration is a statement and every statement in C should end with a semicolon ;

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Declarations …

Syntax for a declaration is:

type var_1, var_2, …,var_n;

E.g: int i, j,k;

Or, write three separate lines like: int i;

int j;

int k;

All the variables that you are using should be declared first.

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Declarations …

Declaration specifies type and also the size (the number of bits that should be allocated to store the declared variable).
These sizes are machine (Hardware) dependant.
Size determines the range of values you can use.

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Declarations …

For example, if size of char is 1 byte (8 bits) then there can be only 2⁸different characters that you can use.
Sizes

char 🡺 1 byte

int 🡺 4 bytes

float 🡺 normally 4 bytes

double🡺 double the size of float

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Declarations …

For some types, you can increase (or decrease) the size relatively by adding some optional qualifiers to the type.
For int 🡺 short int

🡺 long int

For double 🡺 long double

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How to find the size?

sizeof is an operator which you can use.

E.g:

-------------------------

#include<stdio.h>

main()

{

int s;

s = sizeof( int );

printf(“The size of an int is: %d”, s);

}

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sizeof

sizeof is an unary operator.
The operand is either an expression, which is not evaluated, or a paranthesized type name.

int i,j;

j = sizeof i; /* but, j = sizeof int; is wrong */

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Declarations …

Some other qualifiers can be used to specify the range …

E.g: int 🡺 signed int

unsigned int

char can also be signed or unsigned, but this discussion is deferred.

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Declarations…

Some examples:

unsigned short int sum;

if short int is of size 1 byte, what is the range of values that sum can hold ?

long double avg;

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Modifiers in C

The amount of memory space to be allocated for a variable is derived by modifiers.
Modifiers are prefixed with basic data types to modify (either increase or decrease) the amount of storage space allocated to a variable.
For example, storage space for int data type is 4 byte for 32 bit processor. We can increase the range by using long int which is 8 byte. We can decrease the range by using short int which is 2 byte
There are 5 modifiers available in C language. They are,

short
long
signed
unsigned
long long

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Constants

Constants also has type.
1234 is an int
A long int constant is written with a terminal l or L. Eg: 123456789L
An integer too big to fit into an int will also be taken as long.
Unsigned constants are written with a terminal u or U, and the suffix ul or UL indicates unsigned long.

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Constants …

Floating point constants contain a decimal point (123.4) or an exponent (1e-2) or both; and their default type is double, unless suffixed.
The suffixes f or F indicate a float constant;

l or L indicate a long double.

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Constants …

An integer can be specified in octal or hexadecimal instead of decimal.
A leading 0 (zero) on an integer constant means octal; a leading 0x or 0X means hexadecimal.
Eg: decimal 31 = 037 (octal)

= 0x1f = 0X1f (hexa)

What is 0XFUL in decimal?

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Constants …

A character constant is written within a single quotes, like ‘x’
Actually a character is stored as an integer.
The integer value of a character is often called as its ASCII value. (In ASCII character set each character is given an integer value.)
‘0’ 🡪 character zero 🡪 ASCII value is 48
‘0’ is unrelated to the numeric value 0

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Constants

Some characters can not be written normally, hence they have special codes called escape sequences.
‘\n’ 🡪 newline; ‘\a’ 🡪 bell; ‘\\’ 🡪 backslash

‘\t’ 🡪 tab; ‘\0’ 🡪 null

‘\’’ 🡪 single quote; ‘\”’ 🡪 double quote;

There are some more escape characters which you should read in the book as an exercise.

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Constants … (Named constants)

The qualifier const can be applied to the declaration of any variable to specify that its value will not be changed.
Eg: const int sum = 100;

Some other way is through #define directive whose discussion is deferred.

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Input and Output

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int scanf (input)

int i;

char ch;

scanf(“%d”, &i); /* read an integer from stdin into i */

scanf(“%c”, &ch); /* read a char from stdin

into ch */

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scanf (formatted input)

/* both can be read in a single scanf */

scanf(“%d %c”, &i, &ch);

Format string

int variable

char variable

Why there is ‘&’ character before i and ch ?

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Why ‘&’ in scanf ?

Every variable should have a location in the memory.
If i is variable’s name then &i is its address in the memory.
scanf should be given the addresses of the locations where it should store the read values.

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scanf

Different values should be separated with a space or newline.

More about this is deferred.

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int printf (formatted output)

int i; char ch;

i = 125;

ch = ‘a’;

printf(“%d %c \n”, i, ch);

printf(“%c\n%d”,ch,i);

Output on the screen

$./a.out

125 a

125

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printf

char ch = ‘a’;

printf(“%d”, ch);

What will be the output?

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How to read or write a float?

%f 🡪 float

float num;

scanf(“%f ”, &num);

printf(“%f ”, num);