Category: C++ Control Statements

An if statement consists of a boolean expression followed by one or more statements.

Syntax

The syntax of an if statement in C++ is −

if(boolean_expression){// statement(s) will execute if the boolean expression is true}

If the boolean expression evaluates to true, then the block of code inside the if statement will be executed. If boolean expression evaluates to false, then the first set of code after the end of the if statement (after the closing curly brace) will be executed.

Flow Diagram

Example

#include <iostream>usingnamespace std;intmain(){// local variable declaration:int a =10;// check the boolean conditionif( a <20){// if condition is true then print the following
      cout <<"a is less than 20;"<< endl;}
   cout <<"value of a is : "<< a << endl;return0;}

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

a is less than 20;
value of a is : 10

Decision making structures require that the programmer specify one or more conditions to be evaluated or tested by the program, along with a statement or statements to be executed if the condition is determined to be true, and optionally, other statements to be executed if the condition is determined to be false.

Following is the general form of a typical decision making structure found in most of the programming languages −

C++ programming language provides following types of decision making statements.

Sr.No	Statement & Description
1	if statementAn if statement consists of a boolean expression followed by one or more statements.
2	if…else statementAn if statement can be followed by an optional else statement, which executes when the boolean expression is false.
3	switch statementA switch statement allows a variable to be tested for equality against a list of values.
4	nested if statementsYou can use one if or else if statement inside another if or else if statement(s).
5	nested switch statementsYou can use one switch statement inside another switch statement(s).

The ? : Operator

We have covered conditional operator ? : in previous chapter which can be used to replace if…else statements. It has the following general form −

Exp1 ? Exp2 : Exp3;

Exp1, Exp2, and Exp3 are expressions. Notice the use and placement of the colon.

The value of a ? expression is determined like this: Exp1 is evaluated. If it is true, then Exp2 is evaluated and becomes the value of the entire ? expression. If Exp1 is false, then Exp3 is evaluated and its value becomes the value of the expression.