If Else Statement In C Language Ppt

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C Programming Tutorial #06 Conditional Statements: if, if else, cascading if, switch. In 6th lecture of C Programming, we will enter the uncertain world of c. In this guide, we will learn how to use if else, nested if else and else if statements in a C Program. C If else statement. Syntax of if else statement: If condition returns true then the statements inside the body of “if” are executed and the statements inside body of “else” are skipped. When this if-else statement is executed, the string 'bigger value = ' followed by the bigger one among a and b is printed on the output channel (the monitor). 5.4 Condition in an if-else statement The condition in an if-else statement can be an arbitrary expression of type boolean, for example:. a variable of type boolean; Example: boolean. If else statement in C Language with Example Subscribe to updates Unsubscribe from updates If else statement in C language is used when a different sequence of instructions is to be executed depending on the logical value (True / False) of the condition evaluated. If.else.if statement in C programming Consider a situation, where you want to execute a statement based on multiple levels of condition check. For example - At airport there are multi-levels of checking before boarding. First you go for basic security check, then ticket check.

Statements
Labels
label : statement
Expression statements
expression ;
Compound statements
{ statement.. }
Selection statements
if
switch
Iteration statements
while
do-while
for
range for(C++11)
Jump statements
break
continue
return
goto
Declaration statements
declaration ;
Try blocks
try compound-statementhandler-sequence
Transactional memory
synchronized, atomic_commit, etc(TM TS)

Conditionally executes another statement.

Used where code needs to be executed based on a run-time or compile-time condition.

  • 2Explanation

[edit]Syntax

attr(optional)if(condition)statement-true(until C++17)
attr(optional)if(condition)statement-trueelsestatement-false(until C++17)
attr(optional)ifconstexpr(optional)(init-statement(optional)condition)statement-true(since C++17)
attr(optional)ifconstexpr(optional)(init-statement(optional)condition)statement-trueelsestatement-false(since C++17)
attr(C++11) - any number of attributes
condition - one of
  • expression which is contextually convertible to bool
  • declaration of a single non-array variable with a brace-or-equals initializer.
init-statement(C++17) - either
  • an expression statement (which may be a null statement ';')
  • a simple declaration, typically a declaration of a variable with initializer, but it may declare arbitrary many variables or be a decomposition declaration
Note that any init-statement must end with a semicolon ;, which is why it is often described informally as an expression or a declaration followed by a semicolon.
statement-true - any statement (often a compound statement), which is executed if condition evaluates to true
statement-false - any statement (often a compound statement), which is executed if condition evaluates to false

[edit]Explanation

If the condition yields true after conversion to bool, statement-true is executed.

If the else part of the if statement is present and condition yields false after conversion to bool, statement-false is executed.

In the second form of if statement (the one including else), if statement-true is also an if statement then that inner if statement must contain an else part as well (in other words, in nested if-statements, the else is associated with the closest if that doesn't have an else)

Output:


If Statements with Initializer

If init-statement is used, the if statement is equivalent to

{
init_statement
attr(optional)ifconstexpr(optional)(condition)
statement-true

}

or

{
init_statement
attr(optional)ifconstexpr(optional)(condition)
statement-true
else
statement-false

}

Except that names declared by the init-statement (if init-statement is a declaration) and names declared by condition (if condition is a declaration) are in the same scope, which is also the scope of both statements.

(since C++17)

Constexpr If

The statement that begins with if constexpr is known as the constexpr if statement.

In a constexpr if statement, the value of condition must be a contextually converted constant expression of type bool. If the value is true, then statement-false is discarded (if present), otherwise, statement-true is discarded.

The return statements in a discarded statement do not participate in function return type deduction:

The discarded statement can odr-use a variable that is not defined

If a constexpr if statement appears inside a templated entity, and if condition is not value-dependent after instantiation, the discarded statement is not instantiated when the enclosing template is instantiated .

Outside a template, a discarded statement is fully checked. How to add employee discount to anthropologie. ifconstexpr is not a substitute for the #if preprocessing directive:


Note: an example where the condition remains value-dependent after instantiation is a nested template, e.g.

Note: the discarded statement can't be ill-formed for every possible specialization:

The common workaround for such a catch-all statement is a type-dependent expression that is always false:

Labels (goto targets, case labels, and default:) appearing in a substatement of a constexpr if can only be referenced (by switch or goto) in the same substatement.

(since C++17)

[edit]Notes

If statement_true or statement_false is not a compound statement, it is treated as if it were:

is the same as

The scope of the name introduced by condition, if it is a declaration, is the combined scope of both statements' bodies:

If statement-true is entered by goto or longjmp, statement_false is not executed.

switch and goto are not allowed to jump into a branch of constexpr if statement.

(since C++17)

[edit]Keywords

if,else,constexpr

[edit]Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR Applied to Behavior as published Correct behavior
CWG 631 C++98 the control flow was unspecified if first substatement is reached via a label same as in C

Multiple If Else Statements Java

[edit]See also

C documentation for if statement
Retrieved from 'https://en.cppreference.com/mwiki/index.php?title=cpp/language/if&oldid=123390'


Resolving the General Dangling Else/If-Else Ambiguity

A troublesome feature of grammars for many programming languages, including C and C++, is a recurring problem known variously as dangling else, if-else ambiguity, or if-else conflict. We show a way to overcome this problem by syntax alone, yielding a conflict-free syntax without the need for 'disambiguation rules'. In addition, we provide an overview of the algebraic process used to develop the conflict-free syntax. In the following discussion, we use the notation of the AnaGram LALR parser generator to describe the syntax.If Else Statement In C Language Ppt


Description of the Ambiguity

Commonly, the syntax for if-else statements is written thus: where simple statement subsumes expression statements, block statements, break and continue statements, and even the

If Else Statement In C Language Ppt Presentation

do/while statement; in short, any statement which is neither left nor right recursive. loop statement subsumes while statements and for statements, i.e., right recursive statements of the form:This syntax is ambiguous, as can be illustrated by the following example: Using the syntax given above, this statement can be interpreted either as: or as: Both interpretations are consistent with the syntax definition given above, but they have very different outcomes. Conventionally, parsers are rigged using some sort of trick to select the first interpretation. This trick is often called a 'disambiguation rule'. In AnaGram, you could use the sticky attribute statement: However, such tricks are not necessary, since the statement syntax can be made conflict-free as described below. A simpler conflict-free syntax for statements is provided as an example in section 4.3 of 'Compilers: Principles, Techniques and Tools' by Aho, Sethi and Ullman, but their syntax is incomplete in that it does not, in fact, provide for right-recursive statements such as while

If Else Statement In C Language Ppt Presentation

and for

If Else Statement In C Language Ppt Format

.


An Unambiguous Syntax for Statements

The problem with the conventional syntax for statements is that it represents a simple taxonomy of statements rather than an appropriate description of syntax. Although it is true that there are if statements, loop statements and simple statements, this is not the most useful way to classify statements from a syntactic point of view.

The following syntax requires a following else to be paired with the most recent unpaired if, thus disallowing the if-else ambiguity.

We define an open statement as one which has at least one if that is not paired with a following else within the statement. A closed statement either does not contain an if at all, or if it does, the if is paired with a following else. We can then write the statement syntax as follows: In this syntax, we allow only closed statements between an if and its matching else. In other words, between an if and an else an if is allowed only if it is paired with a matching else clause. The net effect is that each else is associated with the nearest preceding if.

In the next section we will show how this syntax can be developed by suitably rewriting our original syntax.


Developing the Conflict-Free Syntax

To see how to resolve the ambiguity and develop the above syntax, let us begin with the customary ambiguous syntax described in the first section and try rewriting statement as where, as described above, open statement is any statement that has a 'dangling' if, that is, an

If Statements In C

if which could be paired with a following else. A closed statement is one which does not have a dangling if.

Substituting the above into the second rule for if statement yields: Clearly, the last of these three rules for if statement is always ambiguous, since open statement, by definition, contains one or more ifs not paired with elses, and thus it is not clear which if should be associated with the else.

Therefore, let us eliminate the last rule, leaving our rules for if statement as follows: One could ask whether it is legitimate to discard a rule so cavalierly. In fact it can be shown, by means of algebraic manipulations too tedious to include here, that all sentences produced by the discarded rule can also be produced by the remaining rules. Thus the discarded rule adds nothing to the grammar but ambiguity.

Now, it remains to determine just which rules for statement belong to open statement and which to closed statement.

To this end, we expand the original rules for statement using the two rules above: The first rule is clearly closed. The second rule is clearly open since it contains at least one unpaired if. The last two rules cannot be classified as they stand, since they would be open or closed depending on whether the final statement were open or closed. Therefore, we expand the final token of the last two rules to yield: Now, we can reorder the above rules: By our definitions, the first three rules are open statements and the last three rules are closed statements. So we can finally rewrite the syntax: yielding the conflict-free syntax presented in the previous section.