An
if statement can be followed by an optional
else statement, which executes when the boolean expression is false.
Syntax:
The syntax of an if...else statement in C++ is:
if(boolean_expression)
{
// statement(s) will execute if the boolean expression is true
}
else
{
// statement(s) will execute if the boolean expression is false
}
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If the boolean expression evaluates to
true then the
if block of code will be executed otherwise
else block of code will be executed.
Flow Diagram:
Example:
#include <iostream>
using namespace std;
int main ()
{
// local variable declaration:
int a = 100;
// check the boolean condition
if( a < 20 )
{
// if condition is true then print the following
cout << "a is less than 20;" << endl;
}
else
{
// if condition is false then print the following
cout << "a is not less than 20;" << endl;
}
cout << "value of a is : " << a << endl;
return 0;
}
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When the above code is compiled and executed, it produces following result:
a is not less than 20;
value of a is : 100
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The if...else if...else Statement:
An
if statement can be followed by an optional
else if...else statement, which is very usefull to test various conditions using single if...else if statement.
When using if , else if , else statements there are few points to keep in mind.
- An if can have zero or one else's 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 he remaining else if's or else's will be tested.
Syntax:
The syntax of an if...else if...else statement in C++ is:
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 the none of the above condition is true.
}
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Example:
#include <iostream>
using namespace std;
int main ()
{
// local variable declaration:
int a = 100;
// check the boolean condition
if( a == 10 )
{
// if condition is true then print the following
cout << "Value of a is 10" << endl;
}
else if( a == 20 )
{
// if else if condition is true
cout << "Value of a is 20" << endl;
}
else if( a == 30 )
{
// if else if condition is true
cout << "Value of a is 30" << endl;
}
else
{
// if none of the conditions is true
cout << "Value of a is not matching" << endl;
}
cout << "Exact value of a is : " << a << endl;
return 0;
}
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When the above code is compiled and executed, it produces following result:
Value of a is not matching
Exact value of a is : 100
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