In this example we will be learning how to use conditional and assignment operator in single expression. In previous chapters we have learnt indirect use of if statement in expression

Use of conditional and assignment operator in expression

Consider below example where we have used the conditional and assignment operator in an expression.

#include <stdio.h>
int main(int argc, char *argv[]) {
   int a = 40, b = 30, c;
   c = !a <= !(c = b);
   printf("%d", c);
   return 0;
}

Output :

1

Explanation

Below is the explanation of the complex expression containing conditional and assignment operators -

Step 1 : Solve the bracket first

While solving an expression, it is thumb rule to solve the bracket first. Lets see how we are solving the brackets -

c = !a <= !(c = b);
c = !a <= !(Assign Value of b to c);
c = !a <= !(30);

so at the end of step 1 our expression will be modified into following expression

c = !a <= !30;

We have replaced the expression (c=b) with 30 in original expression

Step 2 : List our operators with precedence

Now we need to arrange all the operators in the decreasing order of precedence. We are having 2 unary operators, 1 assignment and 1 conditional operator

Re-commanded Article : Operator Precedence and Priority

After listing out all the operators in descending order of priority -

"Not" Operator has higher priority than <= Operator. so we can write it as -

c = !a= !40 = 0

Replace !a by "0" as we calculated it in the above expression statement.

c = 0<=!30

Step 3 : Solve expression recursively

Now again we find there are 3 operators i.e equal to, greater than equal to and Not operator.

"Not" Operator has Higher Priority than any other priority specified in the expression

!30 = 0

so after replacing the expression will be like this -

c = 0 <= 0

Now when we try to solve then we find less than or equal to operator will get higher priority and obviously 0 <= 0 is True condition so it returns 1

c = 1

In this tutorial we are going to see how we can use relational operators in an expression.

Relational operators in an expression

First of all we are going to list out the different relational operators.

Operator,Name of Operator
>,Greater Than
<,Less Than >=,Greater than Operator
<=,Less than Operator ==,Comparison Operator !=,Not equal to Operator [/table]

Use of relational operators in an expression is nothing but using if statement in an expression indirectly

Reading expression containing relational operators

If we use any of the operator listed in above table in your expression then that part of expression will provide you either 0 or 1 as a result. Consider below example -

res = 100 > 20

above expression will assign value 1 to a variable res because relational operators in an expression is used. Consider below example -

Thumb rules for solving expression

Keep in mind simple 2 thumb rules when you find relational operators in an expression -

1. Check whether the expression is true or false. If expression is true then simply replace the expression with 1
2. If expression results into false statement then replace the expression with 0

Examples

Example #1 : Usage of relational operator

#include <stdio.h>
int main(int argc, char *argv[]) {
   int num1 = 100;
   int num2 = 100;
   printf("%d",num1 >  num2);
   printf("%d",num1 >= num2);
   printf("%d",num1 <= num2);
   printf("%d",num1 <  num2);
   return 0;
}

Output :

0 1 1 0

You can see, we have used the relational operators inside the expression and it returns the result with values either 0 or 1. Operation is similar to below statement -

if(num1 > num2)
   printf("1");
else
   printf("0");

Example #2 : Indirect use of if statement

#include<stdio.h>
void main()
{
  int num1 = 100,num2=200,num3;
  num3 = ( num1 >= 100 ) + (num2 < 50 );
  printf("%d",num3);
}

Output :

1

Explanation :

Consider this statement -

num3 = ( num1 >= 100 );

above statement can be written in following way -

if( num1 >= 100 )    
   num3 = 1;
else    
   num3 = 0;

considering above thumb rules we can calculate the value of num3 as -

num3 = ( num1 >= 100 ) + (num2 < 50 );
num3 = 1 + (num2 < 50 );  // ( num1 >= 100 ) is True
num3 = 1 + 0;             // ( num2 <  50  ) is False
num3 = 1;

In the previous chapter we have learnt about the Lvalue of an expression in this chapter we are going to learn R-Value of Expression.

What is R-Value of Expression ?

1. R Value stands for Right value of the expression.
2. In any Assignment statement R-Value of Expression must be anything which is capable of returning Constant Expression or Constant Value.
3. R Value Can be anything of following -

Example of R-Value of Expression

#include<stdio.h>
int main()
{
int num;
num = 5;
return(0);
}

In the above example, Constant Value 5 is assigned to the variable will be considered as right Value of the variable.

Tips : R-Value of Expression

Tip 1 : R value may be constant or constant expression

num = 20;      //Constant RValue
num = 20 + 20; //Constant Expression as RValue

1. In the example, we have assigned constant value to the variable.
2. Constant value “20” is considered as RValue.
3. In the next line we have assigned constant expression to the variable. “20 + 20” will be evaluated first and then result of expression will be assigned to an Variable.

Tip 2 : R value may be MACRO

#define MAX 20
main() {
   int num = MAX;
}

If we have defined a MACRO then we can use MACRO as right value. In the above example we have assigned the 20 to the variable “num”.

In case if we defined the MACRO value of different data type then it may results into compile error.

Tip 3 : R Value may be variable

#define MAX 20
main() 
{
   int flag = 0;
   int num  = flag;
}

For more information , Visit MSDN library.

In the previous chapter we have learnt about C Programming Expressions, in this chapter we will be learning about L-Value of Expression.

What is L-Value of Expression ?

1. L-Value stands for left value
2. L-Value of Expressions refer to a memory locations
3. In any assignment statement L-Value of Expression must be a container(i.e. must have ability to hold the data)
4. Variable is the only container in C programming thus L Value must be any Variable.
5. L Value Cannot be Constant,Function or any of the available data type in C

Diagram Showing L-Value of Expression :

Example of L-Value of Expression :

#include<stdio.h>
int main()
{
  int num;
  num = 5;
return(0);
}

In the above expression, Constant value 5 is being assigned to a variable ‘num’. Variable ‘num’ is called as storage region’s , ‘num’ can considered as LValue of an expression.

Re-commanded Concepts : Concept of Variables and Constants in C

Important Tips :

Below are some of the tips which are useful to make your concept about L-Value of Expression more clear.

Lvalue cannot be a Constant

int main()
{
int num;
5 = num;  //Error
return(0);
}

You cannot assign the value or any constant value to another constant value because meaning of constant is already defined and it cannot be modified.

Lvalue cannot be a Constant Variable

Even we cannot assign a value to a constant variable. Constant variable should not be used as L Value.

int main()
{
const num;
num = 20;  //Error
return(0);
}

Lvalue cannot be a MACRO

We know that macros gets expanded before processing source code by compiler. All the macros will be replaced by defined value using pre-processor before compiling program.

#define MAX 20
int main()
{
MAX = 20;  //Error
return(0);
}

pre-processor will replace all the occurances of macros and hand over modified source code to compiler. following code will be given to compiler after doing pre-processor task

#define MAX 20
int main()
{
20 = 20;
return(0);
}

Re-commanded Reading : Preprocessor macro

Lvalue cannot be a Enum Constant

enum {JAN,FEB,MARCH};
int main()
{
JAN = 20;  //Error
return(0);
}

Lvalue cannot be a Data Type

#define<stdio.h>
#define max 125
struct book{
  char *name;
  int  pages;
};
void main()
{
book = {"C Programming",100};
}

L-Value Require error ?

Causes of Error :

1. Whenever we are trying to assign value to constant value
2. Whenever we are trying to increment or decrement Constant Expression
3. Inside if statement , if we try to write comparison operator as “= =” instead of “==”, then we will get this error.

Solution :

Solution to this problem is very simple -

1. Always try to assign constant value to “Variable“.
2. If you are using comparison operator then we don’t provide space in between operators.

In the next chapter we will be learning RValue of an expression which is also called as right value of an expression.

A. C Programming Expression :

1. In programming, an expression is any legal combination of symbols that represents a value. [Definition from Webopedia]
2. C Programming Provides its own rules of Expression, whether it is legal expression or illegal expression. For example, in the C language x+5 is a legal expression.
3. Every expression consists of at least one operand and can have one or more operators.
4. Operands are values and Operators are symbols that represent particular actions.

Valid C Programming Expression :

C Programming code gets compiled firstly before execution. In the different phases of compiler, c programming expression is checked for its validity.

Priority and Expression :

In order to solve any expression we should have knowledge of C Programming Operators and their priorities.

Types of Expression :

In Programming, different verities of expressions are given to the compiler. Expressions can be classified on the basis of Position of Operators in an expression -

Examples of Expression :

Now we will be looking into some of the C Programming Expressions, Expression can be created by combining the operators and operands

Each of the expression results into the some resultant output value. Consider few expressions in below table