Flow Control and Decision Making Statements

Flow Control and Decision Making Statements

Various control structures are ‒

1. if statement

2. while statement

3. do‒while statement

4. switch case statement

5. for loop

Let us discuss these control structures with the help of simple examples.

1. If statement

• There are two types of if statements ‒simple if statement and compound if statement. The simple if statement is a kind of if statement which is followed by single statement. The compound if statement is a kind of if statement for which a group of statements are followed. These group of statements are enclosed within the curly brackets.

• If statement can also be accompanied by the else part.

• Following table illustrates various forms of if statement.

 

2. while statement

The while statement is executing repeatedly until the condition is false. The while statement can be simple while or compound while. Following table illustrates the forms of while statements –

 

3. do..while

The do...while statement is used for repeated execution. The difference between do while and while statement is that, in while statement the condition is checked before executing any statement whereas in do while statements the statement is executed first and then the condition is tested. There is at least one execution of statements in case of do...while. Following table shows the use of do while statement.

Note that the while condition is terminated by a semicolon.

 

4. switch case statement

From multiple cases if only one case is to be executed at a time then switch case statement is executed. Following table shows the use of switch case statements.

 

5. for loop

The for loop is a not statement it is a loop, using which the repeated execution of statements occurs. Following table illustrates the use of for loop –

1.Break and Continue Statements

• The break and continue statements are used to alter the normal control flow of the program.

Break Statement

• The break statement is used to terminate the loops such as for, while, do...while and switch.

Syntax

break;

Example Program

#include <iostream>

using namespace std;

int main()

{

    int i,count=5;

    for (i = 0; i < 10; i++)

    {

        if (i = = count)

        {

            break;

        }

        cout << "\n i = " << i;

}

}

Output

i = 0

i = 1

i = 2

i = 3

i = 4

Continue Statement

• Sometime we need to skip certain test condition within a loop. At that time continue statement is used.

Syntax

continue;

Programming Example

#include <iostream>

using namespace std;

int main()

{

    int i,count=5;

    for (i = 0; i < 10; i++)

    {

        if (i= = count)

        {

            continue;

        }

        cout << "\n i = " << i;

    }

}

Output

i = 0

i = 1

i=2

i = 3

i = 4

i = 6

i = 7

i= 8

i =9

 

Example :1

Write a program in C++ to find the roots of quadratic equation ax²+bx+c = 0. Use switch.

Solution :

#include <iostream>

#include <cmath> //Used for sqrt()

using namespace std;

int main()

{

    float a, b, c;

    float root1, root2, imaginary;

    float discriminant;

    cout<<"Enter values of a, b, c of quadratic equation  (ax^2 + bx + c): ";

    cin>>a>>b>>c;

    // Calculate discriminant

    discriminant = (b*b) ‒ (4*a*c);

    switch(discriminant > 0)

    {

     case 1:

        //If discriminant is positive

        root1= (‒b+ sqrt(discriminant)) / (2*a);

         root2 = (‒b‒ sqrt(discriminant)) / (2*a);

        cout<<"Two distinct and real roots exists:

         \n root1= "<<<root1<<"\n root2 = "<<root2;

     break;

    case 0:

        //If discriminant is not positive

        switch(discriminant < 0)

        {

        case 1:

           //If discriminant is negative

           root1 = root2 = ‒b/(2*a);

           imaginary = sqrt(‒discriminant) / (2*a);

           cout<<"Two distinct complex roots exists:

           \n root1= "<<root1<<"\n root2 = "<<<root2;

        break;

        case 0:

           //If discriminant is zero

           root1 = root2 root2 = ‒b / (2*a);

           cout<<"Two equal and real roots exists:

           \n root1= "<<root1<<"\n root2 = "<<root2;

        break;

    }

}

return 0;

}

Output

Enter values of a, b, c of quadratic equation

 (ax^2 + bx + c): 4 5 1

Two distinct and real roots exists:

root1=‒0.25

root2 = ‒1

 

Example :2

Write a C++ program to find whether given number is prime or not?

Solution :

#include <iostream>

using namespace std;

int main()

{

   int n, i;

   bool isPrime = true;

   cout << "Enter some number: ";

   cin >> n;

   for(i = 2; i <= n / 2; ++i)

   {

   if(n % i = = 0)

   {

      isPrime = false;

      break;

   }

   }

   if (isPrime)

      cout << "This is a prime number";

   else

      cout << "This is not a prime number";

    return 0;

}

 

Review Question

1.Explain Do‒while with an example.