In programming the order of execution of instructions may have to be changed depending on certain conditions. This involves a kind of decision making to see weather a particular condition has occurred or not and then direct the computer to execute certain instructions accordingly.

Decision making with if statement:

• The if statement is a powerful decision-making statement and is used to control the flow of execution of statements.
  
  
• It is basically a two-way decision statement and is used in conjunction with an expression.
  
  
• It allows the computer to evaluate the expression first and then, depending on weather the value of the expression (relation or condition) is ‘true’ (or non-zero) or ‘false’ (zero), it transfers the control to a particular statement.
  
  

• The if statement may be implemented in different forms depending on the complexity of conditions to be tested. The different forms are:
  
  
  1. ) Simple if statement
  2. ) if……else statement
  3. ) Nested if…….else statement
  4. ) else if ladder

Simple If Statement

where:
statement-block -	may be a single statement or a group of statements.
test_expression -	it is a conditional expression

• If the test_expression is true, the statement-block executed and then statement-x executed; otherwise the statement-block will be skipped and the execution will jump to the statement-x.

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If…..else Statement

• if….else statement is an extension of the simple if statement.

• If the test expression is true, then the true-block statement(s), immediately following the if statements are executed; otherwise, the false-block statement(s) are executed. In either case, either true-block or false-block will be executed, not both.

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If…..else if Ladder

• The if….else statement executes two different codes depending upon whether the test expression is true or false. Sometimes, a choice has to be made from more than 2 possibilities.
  
• The if….else ladder allows you to check between multiple test expressions and execute different statements.

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Nesting of if…..else statement

• Incorporating multiple if-else statements within an if and else statement is known as nesting. Nested if-else in C involves using an if-else statement inside the if statement block.
  

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Conditional Operator

• Useful for making two-way decisions.
  
• Also known as Ternary Operator.
• This operator is a combination of ‘?’ and ‘:’ and takes three operands.

• The conditional_expression is evaluated first.
  
  • If the result is nonzero, expression1 is evaluated and is returned as the value of the conditional expression.
  • Otherwise, expression2 is evaluated and its value is returned.

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goto Statement

• goto statement is known as jump statement in C.
  
• goto is used to transfer the program control to a predefined label.
• goto statement can be used to repeat some part of code for a particular condition.
• goto statement can also be used to break the multiple loops which can not be done by using a single break statement.

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switch Statement

• The control statement that allows us to make a decision form the number of choices is called a switch statement.
  
• The switch statement tests the value of a given variable (or expression) against a list off case value and when a match is found, a block of statement associated with the case is executed.

• break statement at the end of each block signals the end of a particular case and causes an exit from the switch statement.
• default is an optional case. When present, it will be executed if the value of the expression does not match with any of the case value

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