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Decision Making In Cpp
Decision making is about deciding the order of execution of statements based on certain conditions or repeat a group of statements until certain specified conditions are met. C++ handles decision-making by supporting the following statements,
* if statement
* switch statement
* conditional operator statement
* goto statement
* Decision making with if statement
The if statement may be implemented in different forms depending on the complexity of conditions to be tested. The different forms are,
-
Simple if statement
-
If....else statement
-
Nested if....else statement
-
else if statement
Simple if statement
The general form of a simple if statement is,
if( expression )
{
statement-inside;
}
statement-outside;
|
If the expression is true, then 'statement-inside' it will be executed, otherwise 'statement-inside' is skipped and only 'statement-outside' is executed.
Example :
#include<iostream.h>
int main( )
{
int x,y;
x=15;
y=13;
if (x > y )
{
cout << "x is greater than y";
}
} |
Output:
if...else statement
The general form of a simple if...else statement is,
if( expression )
{
statement-block1;
}
else
{
statement-block2;
} |
If the 'expression' is true, the 'statement-block1' is executed, else 'statement-block1' is skipped and 'statement-block2' is executed.
Example :
void main( )
{
int x,y;
x=15;
y=18;
if (x > y )
{
cout << "x is greater than y";
}
else
{
cout << "y is greater than x";
}
} |
Output :
Nested if....else statement
The general form of a nested if...else statement is,
if( expression )
{
if( expression1 )
{
statement-block1;
}
else
{
statement-block2;
}
}
else
{
statement-block3;
} |
if 'expression' is false the 'statement-block3' will be executed, otherwise it continues to perform the test for 'expression 1' . If the 'expression 1' is true the 'statement-block1' is executed otherwise 'statement-block2' is executed.
Example :
void main( )
{
int a,b,c;
clrscr();
cout << "enter 3 number";
cin >> a >> b >> c;
if(a > b)
{
if( a > c)
{
cout << "a is greatest";
}
else
{
cout << "c is greatest";
}
}
else
{
if( b> c)
{
cout << "b is greatest";
}
else
{
printf("c is greatest");
}
}
getch();
} |
else-if ladder
The general form of else-if ladder is,
if(expression 1)
{
statement-block1;
}
else if(expression 2)
{
statement-block2;
}
else if(expression 3 )
{
statement-block3;
}
else
default-statement;
|
The expression is tested from the top(of the ladder) downwards. As soon as the true condition is found, the statement associated with it is executed.
Example :
void main( )
{
int a;
cout << "enter a number";
cin >> a;
if( a%5==0 && a%8==0)
{
cout << "divisible by both 5 and 8";
}
else if( a%8==0 )
{
cout << "divisible by 8";
}
else if(a%5==0)
{
cout << "divisible by 5";
}
else
{
cout << "divisible by none";
}
getch();
} |
***Points to Remember:***
In if statement, a single statement can be included without enclosing it into curly braces { }
int a = 5;
if(a > 4)
cout << "success"; |
No curly braces are required in the above case, but if we have more than one statement inside if condition, then we must enclose them inside curly braces.
== must be used for comparison in the expression of if condition, if you use = the expression will always return true, because it performs assignment not comparison.
Other than 0(zero), all other values are considered as true.
In above example, hello will be printed.
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