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Brief Notes on C

Structure of C program

Include files#include

//for input/output functions Define Constant

#define const_name value main program

main()

{ /* each declarations andstatements are separated by

semi colon */// declarations variables arrays records function declarations etc

// statements}

// function definitions

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Comments are enclosed within

/* comments on multiple lines */// single line comment

Compiler Directives

#includedirective is used to include

the header file for input/output,the standard mathematics library

mat h. hetc.These files are enclosed within < >

#define directive helps in defining

constant symbol

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Datatypes

Standard:int, float, char, double

User defined datatypes:structures, pointers, arrays,enumerated datatype etc.

Declarationintx, y, z;

floatp, q[3][4];charname[20]; array

Expressionx = x + 2 x += 2i = i +1 i++ or ++ix = x +(++i); the value of x is

added with the value of i afterincrementing it by 1.

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x = x + (i++); the value of x isadded with the value of i and then iis incremented by 1.Similarly, x = x+(--i); x = x+(i--);

Example:

/* include header file stdio.h thatcontains I/O functions. */#include // constant definition#define i 6

main(){ // integer declaration

int x, y;// Assignment statementsx=7; y= i + x;

// output statementprintf("%d\n", y);

}

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Conditional Expression

exp ? exp1 : exp2

/* An expression exp is evaluatedand if the value is nonzero (or true -

represented by 1) then expressionexp1 is the final value otherwiseexp2 is the final value of entireexpression. */

Basic Statements

Assignment statement

x = expression

Compound statement{ s1;

s2;. }

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/* Collection of statements, eachseparated by semi colon and

enclosed in brackets */

Conditional statements

i. if (cond) statementii.

if (cond) s1 else s2;

/* Here cond is a boolean conditionwhich can have value 1 (for true) or0 (for false). */

For statement

for (i = m1; i

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While statement

while (cond){ Body };

Do-while statement

do{Body }while cond;

Logical Operators

&& AND|| OR! NOT

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Bitwise operations

& bitwise AND| bitwise inclusive OR^ bitwise exclusive OR right shift

~ One's complement

Relational Operators

== equality

< less than greater than>= greater than equal to

!= Not equality

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Switch statement

switch (exp)

{ case v1 : s1 ; break;case v2 : s2 ; break;

case vn : sn ; break;optional default : s}

/* If the value of expis vjthen sjisexecuted and switch statement isexited using break statement.Execution always starts from 1 tolast. */

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Input/Output statement

/* reads single character and

stores in character variable x */x = getchar();

/* prints single character stored in

x */putchar(x);

/* the following functions are instandard file named stdio.h */

scanf(control, v1, v2, ..);printf(control, e1,e2,...);

Control in input/output

control = "sequence of formatdescriptor"

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Format descriptor Meaning

%d a decimal integer%o a octal integer

%c a single character%s a character string%f a decimal number

(float or double)

\n skip to new line

Examples:

i. printf("%4d%7.2f\n%c\n",x, y, z)ii. scanf("%4d%8.2f \n",&x, &y)

Here & represents memory addresses

Structure in C : Used for recorddeclaration

struct person

{ char name[25];float salary;char address[35];

} p_rec;

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Here p_rec is user defined

structure datatypeDeclaration using above define

structure is as follows:

struct person x, y;

ORp_rec x, y;

Can define structure withinstructureFields of structure variable are

accessed as:

x . salary,y . name etc.

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Subprograms

type fun_name(parameter along

with type){ // local declaration;

body;}

type : is the type of value returnedby the function and can be basic typeor user defined.

return:statement is used in the bodyof a function.

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Example:

#include

main(){ int i, x;

// function declarationint power (x, n);

for (i =0; i < 10; ++i){ x = power(2, i);printf("%d%d\n", i, x);

}}

// function definitionint power(int x, n){ int i, p;

p = 1;for (i =1; i

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Parameter Passing

Default parameter passing is by valueCall by reference can be achieved bypassing addresses as an actualparameters corresponding to pointervariables in formal parameter list.

Pointer variable

int *p, *q, i, t ;float *x, *y;

p & q are pointer variables pointingto locations holding integer values.x & y are pointer variables pointing

to locations holding real values.i and t are simple integer variables.

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Possible Assignments

// initializing pointer variable.

p = NULL/* address of t is stored in pointervariable p. */

t = 2;

p = &t;/* contents of t are added with thatpointed out by p and assigned to i */

i = t + (*p);/* illegal as i is a simple variable and

p is a pointer variable */i = p/* value pointed out by x is assignedto simple variable z */

*x=34.5;

z = *x;/* releasing the memory location

pointed out by p */free(p);

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Illustration of pointer variables:

p 20

q 30

p 30

*p = *q q 30

dangling

p 20

p = q

q 30

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Example: Explainingcall by reference

void swap (int *p,*q){ int t;

t = *p;*p = *q;

*q = t;}

Void type means that the function isnot returning any value. So return

statement is not used when return typeis void.

Corresponding call statementx = 4;

y = 5;// addresses are passedswap(&x, &y);