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Monday, July 27, 2009

Decision Control Statements .

In this post my friend explains about Decision Control Statements in C Language. In programming languages if statement is very useful for decision making.


About the Author

Prasadh Teppala
Embedded Engineer,
India
prasadel06 [at] gmail.com



In program languages if statement is very useful for decision making.

In ‘C’ language the general format for an if statement is:

if ( condition )
{


Simple statement;
Simple statement;
…………….…..;
…………….…..;


}
Here sample statements will execute if and only if condition is true.

Condition Means

1) Normally condition are made with the Relational operators and Logic operators
Relational Operators: > , >= , <, <= , ==, !=.
Logic Operators: &&, || , !

Eg:
if ( i operator j )
One Statement:

Or

If ( i operator j )
{
More statements;
}

Here operator means Relational Operators and Logic Operators.
Here i and j integers, float, characters. Here characters compared by using their ASCII values.

2) Condition is also any number.

Eg:
int a; /* declaration of a */
If( a )
{
a = 10;
}

If we assign ‘0’ to the ‘a’ at the time of declaration , what is the value of the ‘a’ at the end of if block?
Ans: 0 only. 0 is always false.

If we assign ‘-1’ to the ‘a’ at the time of declaration, what is the value of the ‘a’ at the end of if block?
Ans: 10 only. Why Because -1 is true. Any Number other than 0 is always true. The number may be float, double or any.

3) Condition also assignment

Eg:
int a = 5; /* declaration of a */
If( a = 0 )
{
a = 10;
}

Or

int a = 5; /* declaration of a */
a = 0;
If( a )
{
a = 10;
}
Here what is the value of ‘a’? 5 or 0 or 10.
Ans: 0.
Initially ‘a’ was assigned with the 5.
Then in if statement ‘a’ assigned to 0. Therefore value of ‘a’ is 0. Now in place of condition 0 is there. According to the above point No: 2, 0 is always false, therefore the condition is false. The statements inside the ‘if’ block will not execute. There the value of ‘a’ is 0.

4) Condition containing expressions

Eg:
int a = 4; /* declaration and initialization of a */
int b = 2; /* declaration and initialization of b */
If( a/b = = 2 )
{
a = 10;
}
Here first execute the expression a/b which results 2 then it will compare. Therefore ‘a’ value after ‘if’ block is 10. The expressions are of any type and any side of the operator.

Part 2: Decision Control Statements - Part 2

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