Exercise P3.13.

Write a program that asks the user to enter a month (1 for January, 2 for February, and so on) and then prints the number of days in the month. For February, print “28 or 29 days”.

Enter a month: 5

30 days

Solution

#include < iostream >

using namespace std;

int main(){

    int month;
    cout << "Enter a month: " << endl;
    cin >> month;

    if(month == 2){
        cout << "28 or 29 days" << endl;
    }
    else if(month == 4 || month == 6 || month == 9 || month == 11){
        cout << "30 days" << endl;
    } // if month is 1, 3, 5, 7, 8, 10, or 12
    else{
        cout << "31 days" << endl;
    }

}
            

Exercise P3.3.

Write a program that reads in three floating-point numbers and prints the largest of the three inputs. For example:

Please enter three numbers: 4 9 2.5

The largest number is 9.

Solution

#include < iostream >

using namespace std;

int main(){

    /*
        Given three numbers, find the largest
    */

    double n1,n2,n3;

    cout << "Type three numbers: "<< endl;
    cin >> n1 >> n2 >> n3;
    double largest = 0;

    if(n1 >= n2 && n1 >= n3){
        largest = n1;
    }
    else if(n2 >= n1 && n2 >= n3){
        largest = n2;
    }
    else{
        largest = n3;
    }

    cout << "The largest is " << largest << endl;
}
            

Calculating the sum

Please enter a number : 4

The sum is 10.

Solution

/*

    Calculating the sum 1 + 2 + 3 + ... + N 
    using a for loop.

*/

#include < iostream >

using namespace std;

int main()
{

    int num = 0;

    cout << "Please enter a number : ";
    cin  >> num;

    int sum=0;

    for(int i=1;i <= num;++i){
        sum += i;
    }

    cout << "The sum is " << sum << "." << endl;

    return 0;
}
            

Finding the max

Please enter the number of scores : 4

Please enter score 1 : 90

Please enter score 2 : 70

Please enter score 3 : 65

Please enter score 4 : 98

The max is 98.

Solution

/*

    Finding the maximum using a for loop

*/

#include < iostream >

using namespace std;

int main()
{
    int num = 0;

    cout << "Please enter the number of scores : ";
    cin  >> num;

    double max = 0;

    for(int i = 0; i <= num; i++)
    {
        cout << "Please enter score " << i << " : ";

        double score;
        cin  >> score;

        if(score > max)
        {
            max = score;
        }
    }

    cout << "The max is " << max << "." << endl;

    return 0;
}
            

Exercise P3.21.

Exercise P3.21. Prime numbers. Write a program that prompts the user for an integer and then prints out all prime numbers up to that integer. For example, when the user enters 20, the program should print

2

3

5

7

11

13

17

19

Recall that a number is a prime number if it is not divisible by any number except 1 and itself.

Solution

#include < iostream >
#include < string >

using namespace std;

int main(){

    cout << "Type a number : ";
    int num;
    cin >> num;

    for(int i = 2; i <= num; i++)
    {
        bool prime = true;
        for(int j = 2; j < i; j++)
        {
            if(i%j==0)
            {
                prime = false;
                break;
            }
        }
        if(prime)
        {
            cout << i << endl;
        }
    }

    return 0;

}