review

1. Write a program that will

input an integer n

calculate the sum of the positive integers from 1 – n

output  the sum

#include

using namespace std;

main()

{

Int n;

cin >> n;

cout << (n+1)*(n/2.0) << endl;

int sum = 0;

for (int I = 0; I < n; i++)

                sum = sum + I;

counter; loop control variable;  accumulator; flag
2. Write a program that will input an integer n, and determine if n is the sum of the positive integers 1 – k for some positive integer k.

 For example if n=6 it is the sum of the first 3 positive integers:  1+2+3, but if n=5, then there is no positive integer k such that n=1+2+ … +k.

Your program will print one of 2 messages:

If there is such a k, output the following message:

The number n is the sum of the first k positive integers.

For example, if your program inputs  n=6, it should output the message:

The number 6 is the sum of the first 3 positive integers.

If there is no such k, output the following message:  “There is no positive integer k such that n is the sum of the integers 1 through k.

For example, if your program inputs n=5 it should output the message:

There is no positive integer k such that 5 is the sum of the integers 1 through k.

Main()

{

Int n, sum = 0; cin >> n;

For(int I = 1; I <= n; i++)

{

Sum = sum + I;

If (sum == n)

{

Cout << “the sum of the nums 1 thru “ << I << “is” << n;

Break;

}

Else if (sum > n)

{

Cout << “there is no such sum “;

Break;

}

}

3. Assume that you have an array of 100 integers:

int a[100];

a.       Write a loop that will add up the values stored at the even index positions in the array (i.e. 0,2,4, … ).

Int sum =0;

For (int I = 0; I < 100; I+=2)

          Sum += A[I];

b.      Write a loop that will add up the values stored at the even index positions in the array (i.e. 0,2,4, …  ) but only if the value of the elements in those positions are even.

Int sum =0;

For (int I = 0; I < 100; I+=2)

                If ( A[I] % 2 == 0)

                                Sum += A[I];

c.       Write a loop that will add up the values stored at the odd index positions in the array (i.e. 1,3,5, …  ) but only if the value of the elements in those positions are even.

Int sum =0;

For (int I = 1; I < 100; I+=2)

                If ( A[I] % 2 == 0)

                                Sum += A[I];

4. Write a program that inputs an integer n, and outputs all the numbers that divide n. For example, if n=6, output : 1,2 3. Don’t output the number n itself.

For (int I = 0; I < n / 2; i++)

        If (n % I == 0)

                        Cout << I << “ “;

5. Given the following 2 dimensional array with half the elements shaded black and half white.

            int b[8][8]

Write a program segment that will sum up all the elements in the black boxes.

Sum = 0 ;

For (int I = 0; I < 8; I++)

     For (int J = I%2; J < 8; J+=2)

          Sum += A[I][J];