Learn FORTRAN with Real Code Examples

program Counter
    integer :: count = 0
    logical :: isDark = .false.

    print *, 'Counter:', count
    print *, 'Theme:', merge('Dark','Light',isDark)

    ! Increment counter
    count = count + 1
    print *, 'Counter:', count

    ! Toggle theme
    isDark = .not. isDark
    print *, 'Theme:', merge('Dark','Light',isDark)

    ! Decrement counter
    count = count - 1
    print *, 'Counter:', count

    ! Reset counter
    count = 0
    print *, 'Counter:', count
end program Counter

Demonstrates a simple counter with theme toggling using Fortran variables and console output.

program Addition
    integer :: a = 10
    integer :: b = 20
    integer :: sum
    sum = a + b
    print *, 'Sum:', sum
end program Addition

Adds two numbers and prints the result.

program Factorial
    integer :: fact = 1
    integer :: i
    for i = 1, 5
        fact = fact * i
    end for
    print *, 'Factorial:', fact
end program Factorial

Calculates factorial of 5 using a loop.

program Fibonacci
    integer :: fib0 = 0, fib1 = 1, next, i
    print *, fib0
    print *, fib1
    do i = 3, 10
        next = fib0 + fib1
        print *, next
        fib0 = fib1
        fib1 = next
    end do
end program Fibonacci

Generates first 10 Fibonacci numbers.

program MaxNumber
    integer :: a = 15, b = 25, max
    if (a > b) then
        max = a
    else
        max = b
    end if
    print *, 'Max:', max
end program MaxNumber

Finds the maximum of two numbers.

program ArraySum
    integer, dimension(5) :: nums = (/1,2,3,4,5/)
    integer :: sum = 0, i
    do i = 1, 5
        sum = sum + nums(i)
    end do
    print *, 'Sum:', sum
end program ArraySum

Sums elements of an array.

program EvenFilter
    integer, dimension(5) :: nums = (/1,2,3,4,5/)
    integer :: i
    do i = 1, 5
        if (mod(nums(i),2) == 0) then
        print *, 'Even:', nums(i)
        end if
    end do
end program EvenFilter

Prints even numbers from an array.

program ConditionalIncrement
    integer :: count = 3
    if (count < 5) then
        count = count + 1
    end if
    print *, 'Count:', count
end program ConditionalIncrement

Increment counter only if less than 5.

program ResettableCounter
    integer :: count = 0
    count = count + 1
    count = count + 1
    count = count + 1
    print *, 'Count:', count
    count = 0
    print *, 'Count after reset:', count
end program ResettableCounter

Counter that increments and can be reset.

program ThemeToggle
    logical :: isDark = .false.
    print *, 'Theme:', merge('Dark','Light',isDark)
    isDark = .not. isDark
    print *, 'Theme:', merge('Dark','Light',isDark)
    isDark = .not. isDark
    print *, 'Theme:', merge('Dark','Light',isDark)
end program ThemeToggle

Toggles theme multiple times.