Decision Making Statement in C++

In the C++ language decision making statement executes if the given condition is  true otherwise conditional block will never execute.

C++ language assumes non-zero and non-null values as true, and zero or null is assumed as false value.

There are following types of decision making statements in C++ programming language.

if statement

Syntax of an ‘if’ statement −

if(Condition) {
/* statement will execute if the condition is true */
}

In a ‘if’ statement if the Condition is true, then the block of statement of the ‘if’ statement will be executed.

If the Condition is false, then the block of statement of the ‘if’ statement will not executed and control sent to the next line of if block.

Example: Write a program to demonstrate the ‘if’ statement. 

#include 
using namespace std;
int main()
{
	int x = 10;
	int y = 25;

	if (x < y)	// condition x < y is true therefore if block will execute
	{
		cout << "Sum of x+y = " << (x + y);

	}

	cout << "\n after if statement";
	return 0;

}

Output

Sum of x+y = 35
 after if statement

In the above program if reverse the ‘if’ condition of ‘if’ statement then the condition will be false and ‘if’ block will never execute.

#include 
using namespace std;
int main()
{
	int x = 10;
	int y = 25;

	if (x > y)	// condition x>y is false therefore if block will not execute
	{
		cout << "Sum of x+y = " << (x + y);

	}

	cout << "\n after if statement";
	return 0;

}

Output

 after if statement

if-else  statement

Syntax of an 'if-else' statement −

if(Condition) {
/* if-statement will execute if the Condition is true */
}
else
{ if the condition is false then else block will execute
}

In a ‘if-else’ statement if the Condition is true, then the block of statements of the 'if' statement will be executed.

If the Condition is false, then the block of code of the 'else' statement will executed.

Example: Write a program to  take two numbers from user and find the grater between them using ‘if-else’ statement. 

#include 
using namespace std;
int main()
{
	int x;
	int y;
	cout << "enter  1st number";
	cin >> x;	// 10		
	cout << "\n enter  2nd number";
	cin >> y;	// 30

	if (x > y)	// check condition x>y
	{
		cout << "\n grater value=  " << x;
	}
	else
	{
		cout << "\n grater value= " << y;
	}

	return 0;

}

Output

1st number   											10 			// user enter 10  in variable x							enter  2nd number  											30			// user enter  30  in variable y							 grater value=  30

Nested -if statement
In a C language we can use if statement inside another if statement(s).
Syntax of an 'nested -if' statement −


if(condition 1) {
/* statement will execute if the condition 1 is true */
If (condition 2) { /* statement will execute if the condition 2 is true */
}
}

Example: Write a program to take two numbers from user if both number are between 1 to 9 then print “Good” using nested-if statement. 

#include 
using namespace std;
int main()
{
	int x;
	int y;
	cout << "enter  1st number";
	cin >> x;	// 5		
	cout << "\n enter  2nd number";
	cin >> y;	// 7

	if (x < 10)	// check condition x < 10 
	{
		if (y < 10)	// nested-if, check condition y < 10		
		{
			cout << "\n Good";
		}
	}

	return 0;
}

Output

enter  1st number   											5 			// user enter 5  in variable x							enter  2nd number  											7			// user enter  7  in variable y							 Good

Nested if-else statements

In a C language we can use  if or if-else statement inside another if or  if-else statement(s).

Syntax of an 'if-else' statement −

if(condition 1) { /* statement will execute if the condition 1 is true */
If (condition 2) {
/*if- statement will execute if the condition 1 & 2 both are true */
}
else {
/* else-statement will execute if the condition1 is true Condition2 is false */
}
}
else {
If (condition 3) {
/* statement will execute if the condition 3 is true */
}
}

Example: Write a program to  take three numbers from user and find the grater among them using ‘nested if-else’ statement. 

#include 
using namespace std;
int main()
{
	int x;
	int y;
	int z;
	cout << "enter  1st number";
	cin >> x;	// 6		
	cout << "\n enter  2nd number";
	cin >> y;	// 2
	cout << "\n enter  3rd number";
	cin >> z;	// 10

	if (x > y)	// check condition x>y
	{
		if (x > z)	// check condition x>z	
		{
			cout << "\n grater value=  " << x;
		}
		else
		{
			cout << "\n grater value=  " << z;
		}
	}
	else
	{
		if (y > z)	// check condition x>z	
		{
			cout << "\n grater value=  " << y;
		}
		else
		{
			cout << "\n grater value=  " << z;
		}
	}

	return 0;
}

Output

enter  1st number
6				// user enter 6  in variable x	
 enter  2nd number
2				// user enter 2  in variable x	
 enter  3rd number
10				// user enter 10  in variable x	
 grater value=  10
Categories C++