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 assumes any non-zero and non-null values as true, and if it is
either zero or null, then it is
assumed as false value.
C -
if statement
An if statement consists of a boolean expression followed by one
or more statements.
Syntax:
The syntax of an if statement in C programming language 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.
C programming language assumes any non-zero and non-null values as true and if it is either zero or null, then it is
assumed as false value.
Flow Diagram:
Example:
#include <stdio.h>
int main ()
{
/* local variable
definition */
int a = 10;
/* check the boolean
condition using if statement */
if( a < 20 )
{
/* if condition is
true then print the following */
printf("a is
less than 20\n" );
}
printf("value of a
is : %d\n", a);
return 0;
}
When the above code is compiled and executed, it produces
the following result:
a is less than 20;
value of a is : 10
C - if...else statement
An if statement can be followed by an optional else statement, which executes when the boolean expression is
false.
Syntax:
The syntax of an if...else statement
in C programming language is:
if(boolean_expression)
{
/*
statement(s) will execute if the boolean expression is true */
}
else
{
/*
statement(s) will execute if the boolean expression is false */
}
If the boolean expression evaluates to true, then the if block of code will be executed, otherwise else block of code will be executed.
C programming language assumes any non-zero and non-null values as true, and if it is
either zero or null, then it is
assumed as false value.
Flow Diagram:
Example:
#include <stdio.h>
int main ()
{
/* local variable
definition */
int a = 100;
/* check the boolean
condition */
if( a < 20 )
{
/* if condition is
true then print the following */
printf("a is
less than 20\n" );
}
else
{
/* if condition is
false then print the following */
printf("a is
not less than 20\n" );
}
printf("value of a
is : %d\n", a);
return 0;
}
When the above code is compiled and executed, it produces
the following result:
a is not less than 20;
value of a is : 100
The if...else if...else Statement
An if statement can be followed by an optional else if...else statement, which is very useful to
test various conditions using single if...else if statement.
When using if , else if , else statements there are few points
to keep in mind:
·
An if can have zero or one else's
and it must come after any else if's.
·
An if can have zero to many else
if's and they must come before the else.
·
Once an else if succeeds, none of
the remaining else if's or else's will be tested.
Syntax:
The syntax of an if...else
if...else statement in C programming language is:
if(boolean_expression 1)
{
/*
Executes when the boolean expression 1 is true */
}
else if( boolean_expression 2)
{
/*
Executes when the boolean expression 2 is true */
}
else if( boolean_expression 3)
{
/*
Executes when the boolean expression 3 is true */
}
else
{
/*
executes when the none of the above condition is true */
}
Example:
#include <stdio.h>
int main ()
{
/* local variable
definition */
int a = 100;
/* check the boolean
condition */
if( a == 10 )
{
/* if condition is
true then print the following */
printf("Value
of a is 10\n" );
}
else if( a == 20 )
{
/* if else if
condition is true */
printf("Value
of a is 20\n" );
}
else if( a == 30 )
{
/* if else if
condition is true */
printf("Value
of a is 30\n" );
}
else
{
/* if none of the
conditions is true */
printf("None
of the values is matching\n" );
}
printf("Exact
value of a is: %d\n", a );
return 0;
}
When the above code is compiled and executed, it produces
the following result:
None of the values is matching
Exact value of a is: 100
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| Decision Making | Functions | L values and R values | Loops | Nested if statements | Nested loops |
| Nested Switch Statements | Operators | Pointers | Scope Rules |
| Strings | Storage Classes | Structures | Switch Statement |
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