9.3: Counter Controlled Example
- Page ID
- 54281
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)In this example, we will write a Fortran program to find the difference between the sum of the squares and the square of the sum of the first \(N\) natural numbers.
Understand the Problem
In order to find the difference between the sum of the squares and the square of the sum of the first \(N\) natural numbers, we will need to find both the sum of the squares and the square of the sum. For example, the sum of the squares of the first ten natural numbers is,
\[ 1^2 + 2^2 + \dots + 10^2 = 385 \nonumber \]
The square of the sum of the first ten natural numbers is,
\[ \left(1+2+ \dots + 10\right)^2 = 55^2 = 3025 \nonumber \]
Hence the difference between the sum of the squares of the first ten natural numbers and the square of the sum is \(3025 - 385 = 2640\).
The program will display the \(N\) value, the sum of the squares, the square of the sum, and the difference for each number from 2 to a given \(N\) value. The program should prompt for and read the \(N\) value. The program will display appropriate headers.
Create the Algorithm
For this problem, first we will need to read the \(N\) value. Then, we will loop from 1 to the \(N\) value and find both the sum of the squares and the square of the sum.
! declare variables ! integer -> i, n, SumOfSqrs, SqrOfSums ! display initial header ! prompt for and read the n value ! loop from 1 to n ! compute sum of squares ! compute sums ! square the sums ! compute difference between sum of squares and square of sums ! display results
For convenience, the steps are written as program comments.
Implement the Program
Based on the algorithm, the program below could be created.
program SOSdifference
! declare variables
implicit none
integer :: i, n, SumOfSqrs=0, SqrOfSums=0, difference
! display initial header
write (*,*) "Example Program"
write (*,*) " Difference between sum of squares "
write (*,*) " and square of sums"
write (*,*)
! prompt for and read the n value
write (*,*) "Enter N value: "
read (*,*) n
! loop from 1 to n
do i = 1, n
! compute sum of squares
SumOfSqrs = SumOfSqrs + i**2
! compute square of sums
SqrOfSums = SqrOfSums + i
end do
! square the sums
SqrOfSums = SqrOfSums**2
! compute difference between sum of squares and square of sums
difference = SqrOfSums - SumOfSqrs
! display results
write (*,*) "Difference: ", difference
end program SOSdifference
The spacing and indentation are not required, but help to make the program more readable.
Test/Debug the Program
For this problem, the testing would be to ensure that the results match the expected values. Some expected results can be determined with a calculator or a spreadsheet. If the program does not provide the correct result, one or both of the intermediate results, SumOfSqrs or SqrOfSums, may be incorrect. These values can be displayed with a temporary write statement to determine which might not be correct. If the problem is still not found, the intermediate values calculated during the loop can also be displayed with a write statement. The output can be reviewed to determine what the program is doing (and what may be wrong).