YouTipC If Else
# C if...else Statement
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An **if statement** can be followed by an optional **else statement**, which executes when the boolean expression is false.
## Syntax
The syntax of the **if...else** statement in C:
```c
if(boolean_expression)
{
/* statement(s) will execute if the boolean expression is true */
}
else
{
/* statement(s) will execute if the boolean expression is false */
}
If the boolean expression evaluates to **true**, then the code inside the **if** block will be executed. If the boolean expression evaluates to **false**, then the code inside the **else** block will be executed.
C language assumes any **non-zero** and **non-null** value as **true**, and if it is either **zero** or **null**, then it is assumed as **false**.
## Flow Diagram
## Example
```c
#include
int main ()
{
/* local variable definition */
int a = 100;
/* check the boolean condition */
if( a < 20 )
{
/* if condition is true then print the following */
printf("a is less than 20n" );
}
else
{
/* if condition is false then print the following */
printf("a is not less than 20n" );
}
printf("value of a is : %dn", a);
return 0;
}
When the above code is compiled and executed, it produces the following result:
a is not less than 20
value of a is : 100
## if...else if...else Statement
An **if** statement can be followed by an optional **else if...else** statement, which is very useful to test various conditions using a single if...else if statement.
When using if...else if...else statements, there are a few points to keep in mind:
* An if can have zero or one else, and it must come after any else if's.
* An if can have zero to many else if's, and they must come before the else.
* Once an else if succeeds, none of the remaining else if's or else's will be tested.
## Syntax
The syntax of the **if...else if...else** statement in C:
```c
if(boolean_expression 1)
{
/* Executes when the boolean expression 1 is true */
}
else if( boolean_expression 2)
{
/* Executes when the boolean expression 2 is true */
}
else if( boolean_expression 3)
{
/* Executes when the boolean expression 3 is true */
}
else
{
/* Executes when none of the above conditions is true */
}
## Example
```c
#include
int main ()
{
/* local variable definition */
int a = 100;
/* check the boolean condition */
if( a == 10 )
{
/* if condition is true then print the following */
printf("Value of a is 10n" );
}
else if( a == 20 )
{
/* if else if condition is true */
printf("Value of a is 20n" );
}
else if( a == 30 )
{
/* if else if condition is true */
printf("Value of a is 30n" );
}
else
/* if none of the conditions is true */
{
printf("None of the values is matchingn" );
}
printf("Exact value of a is: %dn", a );
return 0;
}
When the above code is compiled and executed, it produces the following result:
None of the values is matching
Exact value of a is: 100
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