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C++ If-Else Statement

An if statement can be followed by an optional else statement, which executes when the boolean expression is false.

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
}

If the boolean expression evaluates to true, then the if block of code will be executed, otherwise else block of code will be executed.

#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;
}

When the above code is compiled and executed, it produces the following result −

a is not less than 20;
value of a is : 100

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.

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.
}

#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;
}

When the above code is compiled and executed, it produces the following result −

Value of a is not matching
Exact value of a is : 100

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