11.10: Example

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This example will scan a string and convert all lower-case letter to upper-case.

Understand the Problem

For this problem, the string will be read from the user with a maximum of 80 characters. Any lower case letters encountered will be converted to upper-case. All other characters (digits, symbols, etc.) will be left alone. To determine if a character is lower-case, we can see if it is between “a” and “z”. The final string will be displayed back to the screen. Based on the ASCII table in Appendix A, there is a specific, fixed difference between each upper and lower-case letter. Thus, in order to convert a lower- case character to upper-case, that difference can be subtracted. However, in order to perform the subtraction, each character needs to be converted into an integer (based on its value in the ASCII table). The IACHAR() intrinsic function performs this conversion. After the conversion (subtraction), the integer must be converted back into its corresponding character, which can be accomplished with the ACHAR() intrinsic function. These functions work on a single character/integer, so each character will need to be addressed individually.

Create the Algorithm

For this problem, first we will need to prompt for and read the input string. Then any trailing blanks will be removed and the final length can be determined. Based on that length, each character will be accessed and converted if needed.

! declare variables
!     integer -> string1, string2, I, strlen
! display initial header
! prompt for string
! read string
! trim any trailing blanks
! determine length of string
! loop
!     access each character
!     if check lower-case ("a" – "z") -> convert to upper-case
! display final string

For convenience, the steps are written as program comments.

Implement the Program

Based on the algorithm, the below program could be created.

program caseConverter

! declare variables
implicit none
integer :: i, strlen
character(80) :: string1

! ----------
! display initial header
    write (*,'(a,/)') "Case Conversion Example"

! ----------
! prompt for string
! read string
    write (*,'(a)',advance="no") "Enter String (80 char max): "
    read (*,'(a)') string1

! ----------
! trim any trailing blanks
! determine length of string
    strlen = len(trim(string1))

! loop
    do i = 1, strlen

    !     access each character
    !     if check lower-case -> convert to upper-case
    
    if ( string1(i:i) >= "a" .and. string1(i:i) <= "z" ) then
        string1(i:i) = achar( iachar(string1(i:i)) - 32)
    end if
    
    end do

! ----------
! display final string

    write (*,'(/,a)') "-------------------------------------"
    write (*,'(a,/,2x,a,/)') "Final String: ", string1

end program caseConverter

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 ensure that the output string is correct for the given input.

For example, the following output,

c:\mydir> case
Case Conversion Example

Enter String (80 char max): Hello World!?

-------------------------------------
Final String:
  HELLO WORLD!?

Each lower-case letter was converted to upper-case while the upper-case, space, and punctuation were unchanged. The program should be executed with a series of test inputs to verify the correct output.