Getting Started

Question 1

Four Important aspects of any language:

Answer 1

1. Way it stores data
2. Way it operates upon it.
3. how it accomplishes input and output.
4. how it lets you control the sequence of execution of instructions in a program.

Question 2

Why is C used in some parts of Operating systems?

Answer 2

Speed of execution.

Device drivers are written in C.

Question 3

Steps of learning C:

Answer 3

1. Alphabets; Digits; Special Symbols.
2. Constants; Variables; Keywords
3. Instructions
4. Program

Question 4

The C character Set

Answer 4

All alphabets, Capital and small.
All digits 0-9
Special Symbols o keyboard [31].
[ ~ is but ` is not valid]

Question 5

Constant, Variable and Keywords:

Answer 5

These formed by the combination of the C character set.
Constants: Entity with a fixed value.
Variables; Entity with changing values.

Question 6

Variable names theory:

Answer 6

The memory locations are given names and since the value stored in these memory keeps changing hence called variable names.
This allows us to retrieve and use the value stored in the memory location.

Question 7

Types of C constant:

Answer 7

1. Primary
   Integer constant; Real Constant; Character Const.
2. Secondary constants
   Array; Structure; Pointer; Union; Enum,..etc

Question 8

Rules Of Integer Constant:

Answer 8

1. Must have at least 1 digit.
2. Must not have a decimal point.
3. Can be +ve or -ve.
4. No sign implies +ve.
5. No commas and blanks allowed.
6. Range: -32768 to 32767 [ depends on Compiler, this
   is for a 16-bit compiler.]

Question 9

Rules for constructing Real Constants:

Answer 9

aka Floating Point Constants.
expressed in 2 forms:
1. Fractional Form:
   a. at least 1 digit.
   b. Decimal point Must.
   c. Can be +ve or -ve, default +ve
   d. No commas, blanks allowed.

2. Exponential Form: [For too small or too big value]
   a. Has mantissa and exponent[separated by e]
   b. Mantissa can be +ve or -ve, Default +ve.
   c. Exponent must have at least 1 digit again maybe +ve or -ve. Dafault is +ve.
   d. Range: -3.4e38 to 3.4e38

Question 10

Rules for Constructing Character Constants:

Answer 10

Character constant has max length of 1 character.

Enclosed in inverted commas, both single inverted, towards left.
like : ‘A’
‘1’
‘@’

Question 11

In a language, the type of variables supported depends on ?

Answer 11

the type of constant supported.

Question 12

Rules for constructing Variable Names:

Answer 12

1. length 31 (some compilers: 247)
2. First char must be alphabet or underscore
3. No commas or blanks are allowed.
4. ONly special symbol allowed is an underscore.

These rules apply for all types of primary and secondary variables.

Question 13

To differentiate between variables what is done?

Answer 13

Type declaration statements.
int varname;
float varname;
char varname;

Question 14

C keywords:

Answer 14

keywords cant be used as var names.
they are already explained to the compiler.
AKA reserved words
There are 32.
auto double int struct break else long switch case enum register typedef char extern return union const float short unsigned continue for signed void default goto sizeof volatile do if static while

Question 15

Compiler Specific keywords:

Answer 15

ANSI said they should be preceded by 2 underscores.

like __near, __far, __asm

Question 16

C program

how do instructions or statements make them?

Answer 16

Each instruction is written as a separate statement.
Therefore, a C program compromises of a series of statements.
They must appear in the order in which we expect them to execute.
To increase readability u can insert blacnk spaces btw words but not btw varnames, constant, keyword.
Statements are entered in small case letters.

Question 17

Statement terminator:

Answer 17

;

Every statement ends with a ;

Question 18

Comments:

Answer 18

Comment enclosed in /* */
can be anywhere, even btw the statement.
To explain code or provide information.

Compiler Completely Ignores it.

Question 19

Can comments be multiline?

Answer 19

Yes

Question 20

Can comments be nested?

Answer 20

NO

Question 21

C is also called as free form cuz:

Answer 21

No specific rules for position at which a statement should be written.

Question 22

Declare a variable:

and whats initialisation?

Answer 22

int n;
int or float or char
Declare before using.
Assigning value to it is intialising.
int i = 10;   /* declared and initialised */

Question 23

function printf()

Answer 23

printf( “”,);

format string may contains format specifiers :
%f to print real value
%d for int
%c for char
%s - char.
%p - address. 
%u - unsigned Integer.

list of variables can contain Expressions.

Question 24

NewLine

Answer 24

Takes cursor to next line.
\n
One of the Escape Sequences.

Question 25

Compilation and Execution:

Answer 25

To type your C program you need an EDITOR.
once written it is necessary to convert it to machine lang(0s, 1s) so machine can execute it. Compiler performs this conversion.

Integrated Development Environment: Provides editor and compiler.

Question 26

scanf() function:

Answer 26

scanf(“%d%f%c”,&int,&real,&char);

ampersand [&] : Address of operator.
&int : We are telling at which memory location should it store the value supplied by user.
User must use blank,tab or newline(enterkey) to separate the inputs.

Question 27

Types of instructions:

Answer 27

1. Type Declaration
2. Arithmetic
3. Control Instruction

Question 28

Is it valid?

int a = b = c = d = 10 ;

order of assigning

Answer 28

Its invalid as u are assigning b to a before defining it.
but
int a,b,c,d; a = b=c = 10; will work.
float a = 1.5, b = a; is fine but
float b = a+ 1.1, a = 1.5; is not.
as we are trying to use before defining it.

Question 29

Operands:

Answer 29

Variables and constants on RHS of = [assignment operator], as these are operated by the arithmetic operators [+,-,*,/].

Question 30

Arithmetic Instructions :

way of assignment

Answer 30

Value on the right of = is assigned to left.
RHS is evaluated using constants and numerical values stored in variable names. This value is assigned on the LHS.
One variable is allowed on LHS

Question 31

Types Of Arithmetic Instructions:

Answer 31

1. Just Integer constants and variables.
2. Real mode
3. Mixed mode [real and integer operands]

Question 32

% operator:

Answer 32

Modulus operator returns remainder, not applied on floats.
Sign of numerator is assigned to the remainder.
5% -2 = 1
-5 % 2 = -1

Question 33

Arithmetic Instruction on char:

Answer 33

1. To store constants in char variable.
char  a; a = 'F';
a will store F's ASCII value i.e 70.
int z; z = a + 'G';
Addition is performed on ASCII values of chars. z = 70+71

Question 34

The one missed operator in C?

Answer 34

Exponentian.
but we can use:
#include 
main()
{
/* 3 raise to 2 */
print("%d",pow(3,2) );
}

Question 35

Integer to float conversion:

Answer 35

Implicit:

Operation on real and integer yields a real, the integer is converted to real and the operation is performed.

Question 36

float a,b,c ;
int s;
s = a * b * c /100 + 32/4 - 3 * 1.1;

discuss conversions:

Answer 36

Type Conversion In Assignments.
during evaluation in RHS everything is promoted to real if it’s not but since s is an int it can’t store real so evaluated value gets demoted to integer and is stored in s.

Question 37

Hierarchy of Operations:

Answer 37

• , / , % > + , - > =

Question 38

Associativity of Operators:

Answer 38

Its of 2 types:
1. Right to left [ = ]
2. Left to right [ +,/,*]
Used to break tie when same priority operators come together, like / , * .
In left to right : Left operand must be unambiguous, not involved in any sub expression. Then its performed early.

Question 39

a = 3/2*5

How will compiler proceed?

Answer 39

/,* have L to R associativity.

but / has its left operand unambiguous hence it is performed earlier then *.

Question 40

Control Instructions:

Answer 40

1. Sequence Control.
2. Selection or Decision Control.
3. Repetition or Loop control Instruction.
4. Case Control.
   These instructions enable us to specify in which order must instructions be executed.
   Determines ‘ Flow Of Control’.