Fortran - 动态数组

  • 简述

    动态数组是一个数组,它的大小在编译时是未知的,但在执行时是已知的。
    动态数组是用属性声明的allocatable.
    例如,
    
    real, dimension (:,:), allocatable :: darray    
    
    必须提到数组的等级,即维度,但是,要将内存分配给这样的数组,您可以使用allocate功能。
    
    allocate ( darray(s1,s2) )      
    
    使用数组后,在程序中,创建的内存应该使用deallocate功能
    
    deallocate (darray)  
    

    例子

    以下示例演示了上面讨论的概念。
    
    program dynamic_array 
    implicit none 
       !rank is 2, but size not known   
       real, dimension (:,:), allocatable :: darray    
       integer :: s1, s2     
       integer :: i, j     
       
       print*, "Enter the size of the array:"     
       read*, s1, s2      
       
       ! allocate memory      
       allocate ( darray(s1,s2) )      
       
       do i = 1, s1           
          do j = 1, s2                
             darray(i,j) = i*j               
             print*, "darray(",i,",",j,") = ", darray(i,j)           
          end do      
       end do      
       
       deallocate (darray)  
    end program dynamic_array
    
    编译并执行上述代码时,会产生以下结果 -
    
    Enter the size of the array: 3,4
    darray( 1 , 1 ) = 1.00000000    
    darray( 1 , 2 ) = 2.00000000    
    darray( 1 , 3 ) = 3.00000000    
    darray( 1 , 4 ) = 4.00000000    
    darray( 2 , 1 ) = 2.00000000    
    darray( 2 , 2 ) = 4.00000000    
    darray( 2 , 3 ) = 6.00000000    
    darray( 2 , 4 ) = 8.00000000    
    darray( 3 , 1 ) = 3.00000000    
    darray( 3 , 2 ) = 6.00000000    
    darray( 3 , 3 ) = 9.00000000    
    darray( 3 , 4 ) = 12.0000000   
    
  • 数据声明的使用

    data语句可用于初始化多个数组,或用于数组部分初始化。
    数据语句的语法是 -
    
    data variable / list / ...
    

    例子

    以下示例演示了该概念 -
    
    program dataStatement
    implicit none
       integer :: a(5), b(3,3), c(10),i, j
       data a /7,8,9,10,11/ 
       
       data b(1,:) /1,1,1/ 
       data b(2,:)/2,2,2/ 
       data b(3,:)/3,3,3/ 
       data (c(i),i = 1,10,2) /4,5,6,7,8/ 
       data (c(i),i = 2,10,2)/5*2/
       
       Print *, 'The A array:'
       do j = 1, 5                
          print*, a(j)           
       end do 
       
       Print *, 'The B array:'
       do i = lbound(b,1), ubound(b,1)
          write(*,*) (b(i,j), j = lbound(b,2), ubound(b,2))
       end do
       Print *, 'The C array:' 
       do j = 1, 10                
          print*, c(j)           
       end do      
       
    end program dataStatement
    
    编译并执行上述代码时,会产生以下结果 -
    
     The A array:
               7
               8
               9
              10
              11
     The B array:
               1           1           1
               2           2           2
               3           3           3
     The C array:
               4
               2
               5
               2
               6
               2
               7
               2
               8
               2
    
  • 使用 Where 语句

    where语句允许您在表达式中使用数组的某些元素,具体取决于某些逻辑条件的结果。如果给定条件为真,它允许在元素上执行表达式。

    例子

    以下示例演示了该概念 -
    
    program whereStatement
    implicit none
       integer :: a(3,5), i , j
       
       do i = 1,3
          do j = 1, 5                
             a(i,j) = j-i          
          end do 
       end do
       
       Print *, 'The A array:'
       
       do i = lbound(a,1), ubound(a,1)
          write(*,*) (a(i,j), j = lbound(a,2), ubound(a,2))
       end do
       
       where( a<0 ) 
          a = 1 
       elsewhere
          a = 5
       end where
      
       Print *, 'The A array:'
       do i = lbound(a,1), ubound(a,1)
          write(*,*) (a(i,j), j = lbound(a,2), ubound(a,2))
       end do   
       
    end program whereStatement
    
    编译并执行上述代码时,会产生以下结果 -
    
     The A array:
               0           1           2           3           4
              -1           0           1           2           3
              -2          -1           0           1           2
     The A array:
               5           5           5           5           5
               1           5           5           5           5
               1           1           5           5           5