Arithmetic in C, Rules of Operator Precedence, Relational Operators, Keywords

Lecture 3

Arithmetic in C

Most C programs perform arithmetic calculations. The arithmetic operators used by C are as follows.

C Operation	Arithmetic Operator	Algebraic Expression	C Expression
Addition	+	f+7	f+7
Subtraction	-	x-y	x-y
Multiplication	*	bm	b*m
Division	/	x/y	x/y
Modulus	%	r mod s	r%s

Table 1: Arithmetic Operators in C

The arithmetic operators are all binary operators. The expression 3+7 contains binary operator + and two operands 3 and 7. Integer division yields an integer result. 17/4 is 4. The modulus operator means the remainder after a division operation. 17%4 is 1.

Parentheses are used in C expressions in much the same manner as in algebra. a*(b+c) means firstly b and c will be added and the sum of their addition will be multiplied by a.

Rules of Operator Precedence

1.    Expressions or portion of expressions contained in pairs of parentheses are evaluated first. In case of nested parentheses, the inner most parentheses will be evaluated first.

2.    Multiplication, division and modulus operations are evaluated next. If an expression contains several *, / or % operations, evaluations proceed from left to right. These operators are on the same level of precedence.

3.    Addition and subtraction are evaluated last.  If an expression contains several + or - operations, evaluations proceed from left to right.

K m=(a+b+c+d+e)/5

K m=a+b+c+d+e/5

What are the differences here?

K y=mx+c

How do you write this expression in C? Any parenthesis required?

K z=pr%q+w/x-y

It is in algebraic format. How will it be written in C? What will be the order of precedence given by the C compiler while it is written in C format?

Decision Making: Relational Operators

Executable C expressions either do actions (calculations or input or output) or make a decision. For example, in a program where the user will put his mark and want to know if he passed or failed, you will have to do three things-

1. Take the mark from the user. Action

2. Compare the mark with a predefined pass mark range. Decision

3. Provide that decision to user. Action

The decision in C is done by a control structure called if. It allows a program to make a decision based on the truth or falsity of some statement of fact called condition.  If the condition is true, the body statement will be executed otherwise not- it will execute the next statement after the if structure.

Conditions in if structures are formed by using relational operators. The relational operators have the same level of precedence and they associate left to right. Only equality operators have a lower level of precedence than others and they also associate left to right.

Relational Operators	Example of C Condition	Meaning of C Condition
==	x==y	x is equal to y
!=	x!=y	x is not equal to y
>	x>y	x is greater than y
>=	x>=y	x is greater than OR equal to y
<	x<y	x is less than y
<=	x<=y	x is less than OR equal to y

Table 2: Relational Operators in C

Note- There is a subtle difference between == and =. In case of =, it is associated from right to left. a=b means the value of b is assigned to a.

Examples evades Clarity

#include <stdio.h>

#include <conio.h>

void main(){

       clrscr();

       int num1, num2;

       printf(“Enter two numbers to compare: ”);

       scanf(“%d %d”, &num1, &num2);

       if(num1 == num2)

              printf(“%d and %d are equal”, num1, num2);

       if(num1 != num2)

              printf(“%d and %d are not equal”, num1, num2);

       if(num1 < num2)

              printf(“%d is less than %d”, num1, num2);

       if(num1 > num2)

              printf(“%d is greater than %d”, num1, num2);

       if(num1 <= num2)

              printf(“%d is less than or equal to %d”, num1, num2);

       if(num1 >= num2)

              printf(“%d is greater than or equal to %d”, num1, num2);

       getch();

}

Keywords

In the above program- int and if are keywords or reserved words in C. You will have to be careful when you are writing program about keywords. You cannot use them as variable names as C compiler processes keywords in a different way. The full set of keywords that you cannot use in variable names or identifiers are given here.

auto

break

case

char

const

continue

default

do

double

else

enum

extern

float

for

goto

if

inline

int

long

register

restrict

return

short

signed

sizeof

static

struct

switch

typedef

union

unsigned

void

volatile

while

_Bool

_Complex

_Imaginary

Qs

1.    Every C program must have a function. What is its name?

2.    What symbols are used to contain the body of the function?

3.    With what symbol every statement ends with?

4.    Which function displays information on the screen? Which header file is required for that function?

5.    Which function takes input from the user?

6.    Which specifier is required to represent integer?

7.    Which keyword is used to make decision?

8.    What are used to make a program readable?