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The if-else Statement

A simple if statement only allows selection of a statement (simple or compound) when a condition holds. If there are alternative statements, some which need to be executed when the condition holds, and some which are to be executed when the condition does not hold. This can be done with simple if statements as follows:

if (disc >= 0.0)
  cout << "Roots are real";
if (disc < 0.0 )
  cout << "Roots are complex";
This technique will work so long as the statements which are executed as a result of the first if statement do not alter the conditions under which the second if statement will be executed. C++ provides a direct means of expressing this selection. The if-else statement specifies statements to be executed for both possible logical values of the condition in an if statement.

The following example of an if-else statement writes out one message if the variable disc is positive and another message if disc is negative:

if (disc >= 0.0)
  cout << "Roots are real";
else
  cout << "Roots are complex";

The general form of the if-else statement is:

if ( condition )
statementT
else
statementF

If the condition is true then statementT is executed, otherwise statementF is executed. Both statementF and statementT may be single statements or compound statements. Single statements must be terminated with a semi-colon.


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Next: Examples of if-else statements Up: Introduction to C++ Programming Previous: Exercises