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C Programming Language Basics PART III

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C – Operator Types

What is Operator? Simple answer can be given using expression 4 + 5 is equal to 9. Here 4 and 5 are called operands and + is called operator. C language supports following type of operators.

  • Arithmetic Operators
  • Logical (or Relational) Operators
  • Bitwise Operators
  • Assignment Operators
  • Misc Operators

Lets have a look on all operators one by one.

Arithmetic Operators:

There are following arithmetic operators supported by C language:

Assume variable A holds 10 and variable B holds 20 then:

Show Examples

OperatorDescriptionExample
+Adds two operands A + B will give 30
Subtracts second operand from the first A – B will give -10
*Multiply both operands A * B will give 200
/Divide numerator by denumerator B / A will give 2
%Modulus Operator and remainder of after an integer division B % A will give 0
++Increment operator, increases integer value by one A++ will give 11
Decrement operator, decreases integer value by one A– will give 9

Logical (or Relational) Operators:

There are following logical operators supported by C language

Assume variable A holds 10 and variable B holds 20 then:

Show Examples

OperatorDescriptionExample
== Checks if the value of two operands is equal or not, if yes then condition becomes true. (A == B) is not true.
!= Checks if the value of two operands is equal or not, if values are not equal then condition becomes true. (A != B) is true.
> Checks if the value of left operand is greater than the value of right operand, if yes then condition becomes true. (A > B) is not true.
< Checks if the value of left operand is less than the value of right operand, if yes then condition becomes true. (A < B) is true.
>= Checks if the value of left operand is greater than or equal to the value of right operand, if yes then condition becomes true. (A >= B) is not true.
<= Checks if the value of left operand is less than or equal to the value of right operand, if yes then condition becomes true. (A <= B) is true.
&& Called Logical AND operator. If both the operands are non zero then then condition becomes true. (A && B) is true.
||Called Logical OR Operator. If any of the two operands is non zero then then condition becomes true. (A || B) is true.
!Called Logical NOT Operator. Use to reverses the logical state of its operand. If a condition is true then Logical NOT operator will make false. !(A && B) is false.

Bitwise Operators:

Bitwise operator works on bits and perform bit by bit operation.

Assume if A = 60; and B = 13; Now in binary format they will be as follows:

A = 0011 1100

B = 0000 1101

—————–

A&B = 0000 1100

A|B = 0011 1101

A^B = 0011 0001

~A  = 1100 0011

Show Examples

There are following Bitwise operators supported by C language

OperatorDescriptionExample
& Binary AND Operator copies a bit to the result if it exists in both operands. (A & B) will give 12 which is 0000 1100
| Binary OR Operator copies a bit if it exists in eather operand. (A | B) will give 61 which is 0011 1101
^ Binary XOR Operator copies the bit if it is set in one operand but not both. (A ^ B) will give 49 which is 0011 0001
~ Binary Ones Complement Operator is unary and has the efect of ‘flipping’ bits. (~A ) will give -60 which is 1100 0011
<< Binary Left Shift Operator. The left operands value is moved left by the number of bits specified by the right operand. A << 2 will give 240 which is 1111 0000
>> Binary Right Shift Operator. The left operands value is moved right by the number of bits specified by the right operand. A >> 2 will give 15 which is 0000 1111

Assignment Operators:

There are following assignment operators supported by C language:

Show Examples

OperatorDescriptionExample
=Simple assignment operator, Assigns values from right side operands to left side operand C = A + B will assigne value of A + B into C
+=Add AND assignment operator, It adds right operand to the left operand and assign the result to left operand C += A is equivalent to C = C + A
-=Subtract AND assignment operator, It subtracts right operand from the left operand and assign the result to left operand C -= A is equivalent to C = C – A
*=Multiply AND assignment operator, It multiplies right operand with the left operand and assign the result to left operand C *= A is equivalent to C = C * A
/=Divide AND assignment operator, It divides left operand with the right operand and assign the result to left operand C /= A is equivalent to C = C / A
%=Modulus AND assignment operator, It takes modulus using two operands and assign the result to left operand C %= A is equivalent to C = C % A
<<=Left shift AND assignment operator C <<= 2 is same as C = C << 2
>>=Right shift AND assignment operator C >>= 2 is same as C = C >> 2
&=Bitwise AND assignment operator C &= 2 is same as C = C & 2
^=bitwise exclusive OR and assignment operator C ^= 2 is same as C = C ^ 2
|=bitwise inclusive OR and assignment operator C |= 2 is same as C = C | 2

Short Notes on L-VALUE and R-VALUE:

x = 1; takes the value on the right (e.g. 1) and puts it in the memory referenced by x. Here x and 1 are known as L-VALUES and R-VALUES respectively L-values can be on either side of the assignment operator where as R-values only appear on the right.

So x is an L-value because it can appear on the left as we’ve just seen, or on the right like this: y = x; However, constants like 1 are R-values because 1 could appear on the right, but 1 = x; is invalid.

Misc Operators

There are few other operators supported by C Language.

Show Examples

OperatorDescriptionExample
sizeof()Returns the size of an variable. sizeof(a), where a is interger, will return 4.
&Returns the address of an variable.&a; will give actaul address of the variable.
*Pointer to a variable.*a; will pointer to a variable.
? :Conditional Expression If Condition is true ? Then value X : Otherwise value Y

Operators Categories:

All the operators we have discussed above can be categorised into following categories:

  • Postfix operators, which follow a single operand.
  • Unary prefix operators, which precede a single operand.
  • Binary operators, which take two operands and perform a variety of arithmetic and logical operations.
  • The conditional operator (a ternary operator), which takes three operands and evaluates either the second or third expression, depending on the evaluation of the first expression.
  • Assignment operators, which assign a value to a variable.
  • The comma operator, which guarantees left-to-right evaluation of comma-separated expressions.

Precedence of C Operators:

Operator precedence determines the grouping of terms in an expression. This affects how an expression is evaluated. Certain operators have higher precedence than others; for example, the multiplication operator has higher precedence than the addition operator:

For example x = 7 + 3 * 2; Here x is assigned 13, not 20 because operator * has higher precedenace than + so it first get multiplied with 3*2 and then adds into 7.

Here operators with the highest precedence appear at the top of the table, those with the lowest appear at the bottom. Within an expression, higher precedenace operators will be evaluated first.

Category Operator Associativity 
Postfix () [] -> . ++ – –  Left to right 
Unary + – ! ~ ++ – – (type) * & sizeof Right to left 
Multiplicative  * / % Left to right 
Additive  + – Left to right 
Shift  << >> Left to right 
Relational  < <= > >= Left to right 
Equality  == != Left to right 
Bitwise AND Left to right 
Bitwise XOR Left to right 
Bitwise OR Left to right 
Logical AND && Left to right 
Logical OR || Left to right 
Conditional ?: Right to left 
Assignment = += -= *= /= %= >>= <<= &= ^= |= Right to left 
Comma Left to right 

C – Flow Control Statements

C provides two sytles of flow control:

  • Branching
  • Looping

Branching is deciding what actions to take and looping is deciding how many times to take a certain action.

Branching:

Branching is so called because the program chooses to follow one branch or another.

if statement

This is the most simple form of the branching statements.

It takes an expression in parenthesis and an statement or block of statements. if the expression is true then the statement or block of statements gets executed otherwise these statements are skipped.

NOTE: Expression will be assumed to be true if its evaulated values is non-zero.

if statements take the following form:

Show Example

if (expression) statement; or if (expression) { Block of statements; } or if (expression) { Block of statements; } else { Block of statements; } or if (expression) { Block of statements; } else if(expression) { Block of statements; } else { Block of statements; }

? : Operator

The ? : operator is just like an if … else statement except that because it is an operator you can use it within expressions.

? : is a ternary operator in that it takes three values, this is the only ternary operator C has.

? : takes the following form:

Show Example

if condition is true ? then X return value : otherwise Y value;

switch statement:

The switch statement is much like a nested if .. else statement. Its mostly a matter of preference which you use, switch statement can be slightly more efficient and easier to read.

Show Example

switch( expression ) { case constant-expression1: statements1;

[case constant-expression2: statements2;]

[case constant-expression3: statements3;]

[default : statements4;]

}

Using break keyword:

If a condition is met in switch case then execution continues on into the next case clause also if it is not explicitly specified that the execution should exit the switch statement. This is achieved by using break keyword.

Try out given example Show Example

What is default condition:

If none of the listed conditions is met then default condition executed.

Try out given example Show Example


Looping

Loops provide a way to repeat commands and control how many times they are repeated. C provides a number of looping way.

while loop

The most basic loop in C is the while loop.A while statement is like a repeating if statement. Like an If statement, if the test condition is true: the statments get executed. The difference is that after the statements have been executed, the test condition is checked again. If it is still true the statements get executed again.This cycle repeats until the test condition evaluates to false.

Basic syntax of while loop is as follows:

Show Example

while ( expression ) { Single statement or Block of statements; }

for loop

for loop is similar to while, it’s just written differently. for statements are often used to proccess lists such a range of numbers:

Basic syntax of for loop is as follows:

Show Example

for( expression1; expression2; expression3) { Single statement or Block of statements; }

In the above syntax:

  • expression1 – Initialisese variables.
  • expression2 – Condtional expression, as long as this condition is true, loop will keep executing.
  • expression3 – expression3 is the modifier which may be simple increment of a variable.

do…while loop

do … while is just like a while loop except that the test condition is checked at the end of the loop rather than the start. This has the effect that the content of the loop are always executed at least once.

Basic syntax of do…while loop is as follows:

Show Example

do { Single statement or Block of statements; }while(expression);

break and continue statements

C provides two commands to control how we loop:

  • break — exit form loop or switch.
  • continue — skip 1 iteration of loop.

You already have seen example of using break statement. Here is an example showing usage of continue statement.

#include main() { int i; int j = 10; for( i = 0; i <= j; i ++ ) { if( i == 5 ) { continue; } printf(“Hello %d\n”, i ); } }

This will produce following output:

Hello 0 Hello 1 Hello 2 Hello 3 Hello 4 Hello 6 Hello 7 Hello 8 Hello 9 Hello 10

C – Input and Output

Input : In any programming language input means to feed some data into program. This can be given in the form of file or from command line. C programming language provides a set of built-in functions to read given input and feed it to the program as per requirement.

Output : In any programming language output means to display some data on screen, printer or in any file. C programming language provides a set of built-in functions to output required data.

Here we will discuss only one input function and one putput function just to understand the meaning of input and output. Rest of the functions are given into C – Built-in Functions

printf() function

This is one of the most frequently used functions in C for output. ( we will discuss what is function in subsequent chapter. ).

Try following program to understand printf() function.

#include <stdio.h> main() { int dec = 5; char str[] = “abc”; char ch = ‘s’; float pi = 3.14; printf(“%d %s %f %c\n”, dec, str, pi, ch); }

The output of the above would be:

5 abc 3.140000 c

Here %d is being used to print an integer, %s is being usedto print a string, %f is being used to print a float and %c is being used to print a character.

A complete syntax of printf() function is given in C – Built-in Functions

scanf() function

This is the function which can be used to to read an input from the command line.

Try following program to understand scanf() function.

#include <stdio.h> main() { int x; int args; printf(“Enter an integer: “); if (( args = scanf(“%d”, &x)) == 0) { printf(“Error: not an integer\n”); } else { printf(“Read in %d\n”, x); } }

Here %d is being used to read an integer value and we are passing &x to store the vale read input. Here &indicates the address of variavle x.

This program will prompt you to enter a value. Whatever value you will enter at command prompt that will be output at the screen using printf() function. If you eneter a non-integer value then it will display an error message.

Enter an integer: 20 Read in 20

A complete set of input output functions is given in C – Built-in Functions

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