Nested If or If-Else Statement in Computer Programming: C Language

In any computer programming, a variation of if or if-else statement is known as nested if statement. When an if or if-else statement is used within another if or if-else statement then this statement is called nested if statement. When an action has to be performed based on many decisions, then this statement is used. So, it is called multi-way decision statement. There can be many variations of nested if statement. A sample is given below:

if(condition)
{
    if or if-else statement
}
else                           
{
    if or if-else statement
}

The syntax of nested if shown below:
if(condition1)
{
if(condition2)
    {
      Statement(s);
     }
else
     {
       Statement(s);
     }
}
else
{
  Statement(s);
}

In this statement the conditions are evaluated from the top to bottom. If the outermost condition i.e., condition1 is true the statement(s) associated with this condition are executed as the inner if part is executed here. If condition2 is true the statement associated with this condition are executed otherwise the else (condition2’s false part) part’s statement(s) are executed. If the condition1 of outermost if statement is false then, else part of this if statements are executed, as shown in the above syntax.

For example, consider the following statements:
if(salary>=25000)
  {
If(age<=65)
    Write: ‘Increment in salary 25%’
else
    Write: ‘Increment in salary 24%’
  }   

In the above example the if-else statement is inside if statement, hence the above statement is called the nested if statement. Here, if salary >= 25000 and age is less than or equal to 65, then the output is "Increment in salary 25%". If salary is >= 25000 and age is above 65 then the output will be "Increment in salary 24%".

Algorithm:
Step1:    Read:A, B, C
Step2:    if(A>B)
if(A>C)
Write: “A is largest”
else
Write: “C is largest”
          [End of if]
else
if(B>C)
Write: “B is largest”
    else
Write: “C is largest”
         [End of if]
    [End of if]
Step3:    Exit

I am writing a C program to find largest number among the three given number.

main()
 {
intA,B,C;
clrscr();
printf(“Enter any three integer number here:\n”);
scanf(“%d%d%d”,&A,&B,&C);
if(A>B)
     {
if(A>C)
    printf(“Number %d is largest”,A);
else
    printf(“Number %d is largest”,C);
      }
else
     {
if(B>C)
    printf(“Number %d is largest”,B);
else
    printf(“Number %d is largest”,C);
     }
getch();
}

Advantages:

• There are situations involving series of decisions where we have to use if or if-else statement in another if or if-else statement. In such situations, nested if statements are used.
• Each and every condition may be evaluated to true or false and may involve expressions of various data types.

Disadvantages:

• The nested if-statements are difficult to understand and modify.
• As the depth of nesting increases, the readability of the program decreases.