Chapter 2

 

C Fundamentals

            The basic elements of C includes c character set, identifiers, keywords, data types, constants, variables, array, declarations, expressions and statements.

 

The C character set:

            C uses uppercase A to Z, the lower case letters a to z, the digit 0 to 9 and certain special characters such as:

! ^ # % & * ( ) ¬ - _ = + \ / [ ] { } ; : ‘ “ , < . > / ? (Blank)

 

Most versions of C also allow using @ $.

 

It can be combination of certain characters such as \n, \t to represent non-printable characters new line, horizontal tab respectively. Such character combination to print non printable character is known as escape sequence.

 

Identifiers:

Identifiers are the names given to various element of program such as variables, functions and arrays. Identifiers consist of letters and digits. Rules are to be followed for identifiers:

• It may consist of character, digits but first character must be an alphabet.
• No comma or blanks are allowed within a variable name.
• No special symbols other than underscore can be used in a variable name.
• The uppercase and lowercase letters are distinct.
• It may begin with underscore too.
• Keywords cannot be redefined as identifiers.

 

E.g. x1, sum_temp, Table etc.

Some invalid identifiers are

1x,”X”, -temp etc.

 

Keywords:

            Keywords are reserved identifiers and they cannot be used as names for the program variables to other user defined program elements. The meanings of the keywords have already been given to the compiler. The keywords are also called reserved words. There are 32 keywords available in C.

 

Some compilers may also include:

ada, far, near, asm, fortran, pascal entry, huge

 

Keywords must be in lowercase

 

Constant:

            Constant is a basic element of C which doesn’t change its value during execution of program.

 

Four basic types of constant are:

1. Integer constant

      An integer constant refers to a sequence of digits. It requires minimum 2 bytes and maximum 4 bytes. It could either be positive, negative or zero.

e.g. 10, -30 etc.

Generally, it is of 3 types.

1. Decimal integer

It consists of a set of digits, 0 through 9, preceded by an optional – or + sign.

e.g. 123 0 +78 -312

Spaces, commas and non-digit characters are invalid.

2. Octal Integer:

It consists of any combination of digits from the set 0 through 7, with a leading 0.

e.g. 0 0234 0354 etc

      c. Hexadecimal integer

            A sequence of digits preceded by Ox or OX is considered as hexadecimal integer. They may also include alphabet through A to F as number from a=10 to f=15

 

Rules for constructing integer constant.

1. It must not have a decimal point.
2. It could be either positive or negative
3. If no sign precedes an integer constant it is assumed to be positive.
4. No commas or blanks are allowed within an integer constant.
5. The allowable range for integer constants is -32768 to 32767(16)
6. For 32 bit computer, range will be larger.

 

2. Real constant or floating point constants

            A number with a decimal point and an optional preceding sign represents a real constant.

e.g. 34.8, .2, 0.56 etc

            The real constants could be written in two forms, Fractional form and Exponential form.

Fractional part

            It must have a decimal point. It could be either positive or negative. No commas or blanks are lowed within a real constant.

e.g. +325.34 , -32.76 etc

 

Exponential part

            It is usually used if the value of the constant is either too small or too large. Here, the real constant is represented in two parts. The part appearing before’ is called mantissa, where the part following ‘e’ is called exponent.

           

E.g. +3.2 e-5

            4.1e8 etc

 

Rules for real constants expressed in exponential form.

a.      The mantissa part and the exponent part should be separated by a letter e.

b.     The mantissa part may have positive or negative.

c.      Default sign of mantissa part is positive.

d.     Range of real constants expressed in exponential form is -3.4e38 to 3.4e38.

E.g.  +3.2e^-5,  4.1e⁸ etc.

3. Character Constants.

            A character represented within a single quotes denotes a character constants e.g.’A’,’2’ etc.

            The maximum length of a character constant is one character.

e.g. ‘a’ is a character constant.

4. String constant

            String constants are sequence of characters enclosed within a double quote marks.

e.g. “hello”, “Nepal” etc.

 

 

Variables-

            A variable is a value that can change any time. It is a memory location used to store a data value. Variables hold different kinds of data and the same variable might hold different values during the execution of a program. A variable name should be carefully chosen by the programmer so that its use is reflected in a useful way in the entire program. Variable names are case sensitive.

            Any variable declared in a program should confirm to the following.

·       They must always begin with a letter, although some systems permit underscore as the first character.

·       The length of a variable must not be more than 8 characters.

·       White space is not allowed.

·       A variable should not be a keyword.

·       It should not contain any special characters.

examples of INVALID names are:

567

“a

(name)

*12a

 

            A variable is an entity that has a value and is known to the program by its name.

E.g. f=1.8*c+32

Here, f and c are variables.

 

Declaration of Variables

Every variable used in the

 

1. Basic data types

char, int float are the basic data types.

In C, you always have to declare a variable before using it.

 

sizeof ()

            C provides an operator named sizeof () that gives the number of bytes associated with a specified data type or a variable.

The sizeof () operator takes either a variable or a type name as an argument and returns the number of bytes in that argument.

 

/* illustrating the sizeof () operator */

 

#include<stdio.h>

void main ()

{

int a;

printf (“The size of a is %d\n”, sizeof (a));

printf(“The size of int is %d’, sizeof(int));

}

 

Output:

The size of a is 2

The size of int is 2

 

Const qualifier-

Whenever we want some value of an object to be unchanged throughout the execution of the program, we can use const qualifier. Const is a compile time concept. It just ensures that the object is not modifiable.

 

/* program to illustrate the use of const */

 

#include<stdio.h>

void main()

{

const float pi=3.14;

float radius, area;

printf(“Enter the value of radius\n”);

scanf(“%f”, &radius);

area=pi*radius*radius;

printf(“The area of circle is %f”, area);

}

 

Output:

Enter the value of radius

2.3

The area of circle is 16.610600

 

Another way to achieve the effect of const identifier is by the use of

#define preprocessor directive as:

 

/*program to show the use of #define */

 

#include<stdio.h>

#define pi 3.14

void main()

{

 float radius, area;

printf(“Enter the value of radius\n”);

scanf(“%f”, &radius);

area=pi*radius*radius;

printf(“The area of circle is %f”, area);

}

 

Output:

Enter the value of radius

2.3

The area of circle is 16.610600

 

Preprocessor directive is not terminated by semicolon. The directive instructs all the preprocessor to substitute 3.14 for all the occurrences of the identifier-

const- treats as a value cannot be changed

preprocessor- replaces all of pi by 3.14

 

Operator

 

Arithmetic Operators

 

The major arithmetic operators are addition, subtraction, multiplication and division. Each of the four arithmetic operators is sometimes called a binary operator because it operates on two values at a time.

 

Integer arithmetic

            When two operands such as a and b are declared as integers, an arithmetic operation performed on these integers is called integer arithmetic. It gives integer value as output.

 

/* program that shows integer arithmetic operator */

 

#include<stdio.h>

void main()

{

int a=10, b=5,ans;

ans =a + b;

printf (“a + b=%d\n”, ans);

ans =a-b;

printf (“a - b=%d\n”, ans);

ans =a*b;

printf (“a * b=%d\n”, ans);

ans =b/a;

printf (“b / a=%d”, ans);

}

 

Output:

a + b=15

a - b=5

a * b=50

b / a=0

 

When you divide 5 by 10, the answer is 0.5 but our output is 0.

In C, when one integer is divided by another integer, the result is displayed as an integer. Any fractional part is discarded. Therefore instead of printing 0.5 this program prints out only the integer portion, 0. This process is called truncation.

 

 

Division and modulo division (%) have different meaning from whatever we studied in mathematics.

Division operator gives quotient while modulo division gives remainder after division.

 

/* program that shows / and % operator */

 

int a=7, b=2, ans1, ans2;

ans1=a/b;

ans2=a % b;

printf (“The result of a/b is %d\n”, ans1);

printf (“The result of a %%b is %d”, ans2);

}

 

Output:

The result of a/b is 3

The result of a %b is 1

 

 

Floating point arithmetic

            Floating point arithmetic involves operands of real type in decimal notation.

 

/* floating point arithmetic */

 

float a=19.0, b=9.0,ans;

ans =a/b;

printf (“a / b=%f \n”, ans);

ans =b/a;

printf (“b / a=%f”, ans);

ans =a + b;

printf (“a + b=%f\n”, ans);

 

Output:

a /b=2.111111

b /a=0.473684

a + b=28.000000

Mixed mode arithmetic-

           

Operation	Result
7.0/2 7/2.0 7.0/2.0 7/2	3.5 3.5 3.5 3

 

x=5* 6.7

 

In this, one operand is of type int and another is of type float. In C, this is not considered as an error. The integer value is automatically converted to type double for the calculation; this is known as implicit conversion.

E.g.

int a=2,ans;

float b=12.34,result;

result =a*b;

printf(“%d*%f=%f\n”, a, b, result);

printf)”%f in scientific notation is %e\n”, result, result);

ans =a*b;

printf (“%d*%f=%d\n”, a, b, ans);

}

 

Output:

2*12.340000 24.680000

24.680000 in scientific notation is 2.468000E⁺⁰¹

2*12.340000=24

 

 

In C, there is the choice of explicitly specifying how the values are to be converted in a mixed mode operation. This feature is known as explicit conversion and may be accomplished using cast operator. The name of the data type to which the conversion is to be made (such as int or float) is enclosed in parentheses and placed directly to the left of the value to be calculated.

 

E.g

int a=7;

float b;

b=(float)a+1.0;

printf(“a+1.0 is %f”,b);

}

Output:

A+1.0=8.000000

 

 

 

 

 

Precedence and Associativity of Operators=

 

Operators have rules of precedence and associativity that are used to determine how expressions are evaluated.

 

1+2*3

 

In C, * has higher precedence than +, causing the multiplication to be performed first then the addition. Hence the value of expression is 7.

1 + (2*3)

On other hand, expression inside parentheses are evaluated first, the expression

(1+2)*3 i.e. 9

Now, consider the expression

1+2-3+4-5

Because the binary operators + and – have the same precedence, the associativity rule”left to right” is used to determine how it is evaluated.

 

Priority                                   Operators                                Associativity

1^st                                             (  )                                          L ->R

2^nd                                           *   /   %                                   L ->R

3^rd                                            +   -                                         L ->R

4^th                                            =                                              R ->L

 

 

 

 

Increment and Decrement operator

 

The increment ++ and decrement – are called unary operators. Since these two operators are used with single operand.

 E.g. a++ (postfix operator)

        ++a (prefix operator)

 

#++ and – as a postfix operator

 

When operand is followed by unary operator (++ or --), it is called postfix expression. In postfix expression, assignment takes place first and then variable is incremented or decremented by 1.

For e.g.

 int a=5, b;

b=a++;

 

Here, the value of variable a is assigned to b first then the value of the variable a is incremented. Thus the value of b will be 5 and value of a will be 6 after the evaluation of whole expression.

 

int a=5,b;

b=a--;

Here, the value of variable a is assigned to b first then the value of the variable a is decremented. Thus the value of b will be 5 and the value of a will be 4 after the evaluation of the whole expression.

E.g.

 int a=5,b;

int c=5,d;

b=a++;

printf(“The a value is %d and b value is %d”, a, b);

d=c--;

printf(“The c is %d and d is %d”, c, d);

}

 

Output:

 

The a value is 6 and b value is 5

The c is 4 and d is 5

 

 

# ++ and – as a prefix operator

 

When operator precedes an operand, it is called prefix expression. In prefix expression, increment takes place first and then the incremented value is assigned.

For. E.g.

int a=5,b;

b=++a;

 

Here, the value of variable a is incremented first and then it is assigned to variables b. The value of b will be 6 and value of a will also is 6.

            int a=5,b;

            b=--a;

 

The value of a is decremented first and then it is assigned to variable b. Thus the value of b will be 4 and a will also be 4 after the evaluation of whole expression.

 

Assignment Operator

 

C treats = as an assignment operator. Its precedence is lowest among all the operators we discussed so far and its associativity is right to left.

E.g.

a=2;

b=a*2+a;

In first, 2 is assigned to variable a. Therefore, the value of ‘a’ becomes 2.

In second, a is multiplied by 2 and is added with value of ‘a’ i.e. 2.

 

Thus the result is 6 and is assigned to variable b with the help of assignment operator.

Lets take an e.g. of multiple assignment.

Let i and j are integer variables

 

i=j=5;

Will cause the integer value 5 to be assigned to both i and j. To be more precise, 5 is first assigned to j and the value of j is then assigned to i.

E.g.

1. i=5.4

2. i=j=7

i=j/3=2

1. i=j=7
2. if i=4*j/3         =9
3. i=2*(j/3)         =6

 

In addition to =, there are other assignment operators such as

+ = ,  - = ,  * = , / = , % =

 

Expression                  Equivalent

i* = 5                           i=i+5

i- =j                             i=i-j

j*=(i-3)                       j=j*(i-3)

f/=3                             f=f/3

i %=(j-2)                     i=i%(j-2)

 

Relational Operators

Relational operators are symbols that are used to test the relationship between two variables or between a variable and a constant. C has six relational operators.

 

Operator                                  Meaning

= =                                           Equal to

>                                              Greater than

<                                              Less than

!=                                            Not equal to(either greater than or less than)

>=                                            Greater than or equal to

<=                                            Less than or equal to

 

Note: The assignment operator = and equality operator = = are distinctly different. The assignment operator is used to assign a value to an identifier.

The equality operator = = means:

e.g.(n==7) means ‘Is the value contained in the variable n equal to 7?’ The answer to this is either yes or no.

 

 

Logical Operators:

            C has the following three logical operators.

 

Operators                    Meaning

&&                              Logical AND

||                                  Logical OR

!                                   Logical NOT

 

The logical operators && and || are used to combine expressions containing relational operators.

For E.g. to program

If n is equal to 7 and x is greater than 5. To code this, logical operators called AND are used. The AND is represented by a symbol &&.

i.e. (n==7) && (x>5)

An expression of this kind, which combines two or more relational expressions two or more relational expressions is termed as logical expression or a compound relational expression.

E.g. if(x>y && x>z)               x is highest

      if (x==0 || x==1)               x is binary

 

 

The logical operator OR, is used when at least one f two conditions must be true. The OR is represented by ||.

e.g. if n is equal to 7 or x is greater than 5 can be written as (n==7) || (x>5)

 

# Precedence of Operators

 

Operator                               Associativity

 

( )                                            L to R

! – (unary)                               R to L

* / %                                       L to R

+ - (binary)                             L to R

< <= > >=                                L to R

= =   !=                                    L to R

& &                                         L to R

| |                                             L to R

=                                              R to L

 

 

Conditional Operators (ternary Operators)

The conditional expression is represented by the? and: symbols. It is also called ternary operator because it operates upon three values. The form of conditional expression is

e1? e2:e3

 

If the value e1 is true, the value e2 is returned by the operator? : If e1 evaluates false, the value returned is that of e3.

E.g. j = (i>4)?200:100

If the value of i is 5. Since the expression (I>4) evaluates to true, the value 200(before colon) is returned by the? : Operator and so assigned to j. If the value is say 3, the expression (i>4) evaluates false. Therefore 100 (after colon) is returned and assigned to j.

 

i>4       ?          200      :           100

 

 

Comma Operator

 

The comma operator is used to link the related expression together. A chain of comma in an expression is evaluated from left to right and the value of right most expression is the value of combined expression.

E.g

Value = ( x=10, y=5, x+y);

 

Bitwise Operator

 

These operators operate on bit level. These can only be applied to integer operands whether signed or unsigned.

Operator          Operation performed

>>                    Right shift

<<                    Left shift

~                      1’s complement

&                     Bitwise AND

^                      Bitwise exclusive OR

|                       Bitwise Inclusive OR

 

 

Special Operators

 

Sizeof operator

* and ->           pointer

. and -> structure and union

 

 

Statement

A statement is a part of a program that can be executed. A statement causes the computer to carry out some action. In C, there are five different classes of statements. They are:-

 

1. Expression statement
2. Block statement
3. Control statement
4. Assignment statement
5. Input/Output statement

 

 

1. Expression statement

 

An expression consists of an expression followed by a semi colon. The execution of an expression statement causes the expression to be evaluated.

E.g. ++i;

 

Expression in C can be classified as lvalues and rvalues. The lvalues refers to an expression that has a location in memory. For example, the name of a variable is an lvalues. Modifiable lvalues can be used on the left-hand side of an assignment statement.

The rvalue can be evaluated but cannot be changed. E.g. ‘5’ is rvalue. If a variable x is previously declared, the expression x+3 is also rvalue. It is used on right-hand side.

 

2. Block statement

Block statements are groups of related statements that are treated as a unit. The statements that make up a block are logically bound together. Block statements are also called compound statement.

A block begins with a {and terminated by its matching}.

 

3. Control statement

The program makes a decision about what to do next.

The program needs logical condition to determine if certain conditions are true or false, they do require the repeated execution of groups of statements and they involve the execution of individual groups of statements on a selective basis.

 

 

4. Assignment statement

Statements where results of calculation are stored. The value of the expression on the right of the equal sign to be assigned to the variable on the left.

 

5. Input/Output statement

Data is read in or printed out.

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