Fortran90 Reading and filling in arrays from data file - multidimensional-array

Question

I am supposed to read in this file and fill in the arrays from that data file. But every time i try to run it, i receive an error saying i have invalid memory. The file looks like this
4
SanDiego
0
350
900
1100
Phoenix
350
0
560
604
Denver
900
560
0
389
Dallas
1100
604
389
0
It is basically a traveling salesman algorithm that takes gives the best distance. Here is my whole code
Program P4
IMPLICIT NONE
!Variable Declarations
INTEGER :: count, i, j, ios, distance=0, permutations=0, best_distance
CHARACTER(50) :: filename
TYPE city
CHARACTER(20) :: name
END TYPE
TYPE(city), ALLOCATABLE, DIMENSION(:) :: city_list
INTEGER, ALLOCATABLE, DIMENSION(:,:) :: d_table
INTEGER, ALLOCATABLE, DIMENSION(:) :: path, best_path
PRINT *, "Enter filename"
READ *, filename
!Open the file and read number of cities
OPEN(UNIT = 15, FILE = filename, FORM="FORMATTED", ACTION="READ", STATUS="OLD", IOSTAT=ios)
IF(ios /= 0) THEN
PRINT *, "ERROR, could not open file.", TRIM(filename), "Error code: ", ios
STOP
END IF
READ (UNIT=15, FMT=100) count
PRINT *, "Number of cities: ", count
!Allocate memory for all needed arrays
ALLOCATE(city_list(1:count), d_table(1:count,1:count), best_path(1:count), path(1:count), STAT=ios)
IF(ios /= 0) THEN
PRINT *, "ERROR, could not allocate memory."
STOP
END IF
!Fill in arrays from data file
DO i=1, count
path(i) = i
READ(UNIT=15, FMT=200) city_list(i)
IF(ios < 0) THEN
EXIT
END IF
DO j=1, 4
PRINT *, i, j, city_list(i)
READ(UNIT=15, FMT=100) d_table(i,j)
END DO
END DO
!Use recursion to find minimal distance
CALL permute(2, count)
!Print formatted output
PRINT *
DO i=1, count
PRINT *, path(i)
END DO
DO i=1, count
PRINT *, (city_list(i))
END DO
DO i=1, count
DO j=1, count
PRINT *, d_table(i,j)
END DO
END DO
100 FORMAT (I6)
200 FORMAT (A)
CONTAINS
!Permute function
RECURSIVE SUBROUTINE permute(first, last)
!Declare intent of parameter variables
IMPLICIT NONE
INTEGER, INTENT(in) :: first, last
INTEGER :: i, temp
IF(first == last) THEN
distance = d_table(1,path(2))
PRINT *, city_list(1)%name, city_list(path(2))%name, " ", d_table(1, path(2))
DO i=2, last-1
distance = distance + d_table(path(i),path(i+1))
print *, city_list(path(i))%name, " ", city_list(path(i+1))%name, d_table(path(i),path(i+1))
END DO
distance = distance + d_table(path(last),path(1))
PRINT *, city_list(path(last))%name," ",city_list(path(1))%name, d_table(path(last),path(1))
PRINT *, "Distance is ",distance
PRINT *
permutations = permutations + 1
IF(distance < best_distance) THEN
best_distance = distance
DO i=2, count
best_path(i) = path(i)
END DO
END IF
ELSE
DO i=first, last
temp = path(first)
path(first) = path(i)
path(i) = temp
call permute(first+1,last)
temp = path(first)
path(first) = path(i)
path(i) = temp
END DO
END IF
END SUBROUTINE permute
END PROGRAM P4
And i am no longer gettting an error message and able to run the program, but it its not running properly, it is supposed to out put this
Number of cities: 4
28 San Diego Phoenix 350
29 Phoenix Denver 560
30 Denver Dallas 389
31 Dallas San Diego 1100
32 Distance is 2399
33
34 San Diego Phoenix 350
35 Phoenix Dallas 604
36 Dallas Denver 389
37 Denver San Diego 900
38 Distance is 2243
39
40 San Diego Denver 900
41 Denver Phoenix 560
42 Phoenix Dallas 604
43 Dallas San Diego 1100
44 Distance is 3164
45
46 San Diego Denver 900
47 Denver Dallas 389
48 Dallas Phoenix 604
49 Phoenix San Diego 350
50 Distance is 2243
51
52 San Diego Dallas 1100
53 Dallas Denver 389
54 Denver Phoenix 560
55 Phoenix San Diego 350
56 Distance is 2399
57
58 San Diego Dallas 1100
59 Dallas Phoenix 604
60 Phoenix Denver 560
61 Denver San Diego 900
62 Distance is 3164
63
64
65 San Diego to Phoenix -- 350 miles
66 Phoenix to Dallas -- 604 miles
67 Dallas to Denver -- 389 miles
68 Denver to San Diego -- 900 miles
69
70 Best distance is: 2243
71 Number of permutations: 6
But instead it out puts this
Enter filename
data.txt
Number of cities: 4
1 1 SanDiego
1 2 SanDiego
1 3 SanDiego
1 4 SanDiego
2 1 Phoenix
2 2 Phoenix
2 3 Phoenix
2 4 Phoenix
3 1 Denver
3 2 Denver
3 3 Denver
3 4 Denver
4 1 Dallas
4 2 Dallas
4 3 Dallas
4 4 Dallas
SanDiego Phoenix 1100
Phoenix Denver 604
Denver Dallas 389
Dallas SanDiego 0
Distance is 2093
SanDiego Phoenix 1100
Phoenix Dallas 604
Dallas Denver 0
Denver SanDiego 389
Distance is 2093
SanDiego Denver 1100
Denver Phoenix 389
Phoenix Dallas 604
Dallas SanDiego 0
Distance is 2093
SanDiego Denver 1100
Denver Dallas 389
Dallas Phoenix 0
Phoenix SanDiego 604
Distance is 2093
SanDiego Dallas 1100
Dallas Denver 0
Denver Phoenix 389
Phoenix SanDiego 604
Distance is 2093
SanDiego Dallas 1100
Dallas Phoenix 0
Phoenix Denver 604
Denver SanDiego 389
Distance is 2093
1
2
3
4
SanDiego
Phoenix
Denver
Dallas
1100
1100
1100
1100
604
604
604
604
389
389
389
389
0
0
0
0

Answer 1

When you first open the file, the READ command reads the first line. If you call READ again, you will read line two.
I think that this error comes because you are trying to READ the first line (for the second time) but you are actually reading the second line that is a STRING.
You have two options to fix the error in line 39 (READ statement):
Call the OPEN statement (before the line 39) for a second time in order to READ the first line
Or delete the READ statement because you have already read "count" before (best option in my opinion)
Update:For segmentation fault error
I maid the following changes:
Comment line 39 (to solve the first problem)
In line 42: FMT=200
In line 46: DO j=1, 4 (because between the cities names there are only 4 numbers)
The following code worked for me:
Program P4
IMPLICIT NONE
!Variable Declarations
INTEGER :: count, i, j, ios, distance=0, permutations=0, best_distance
CHARACTER(50) :: filename
TYPE city
CHARACTER(20) :: name
END TYPE
TYPE(city), ALLOCATABLE, DIMENSION(:) :: city_list
INTEGER, ALLOCATABLE, DIMENSION(:,:) :: d_table
INTEGER, ALLOCATABLE, DIMENSION(:) :: path, best_path
PRINT *, "Enter filename"
READ *, filename
!Open the file and read number of cities
OPEN(UNIT = 15, FILE = filename, FORM="FORMATTED", ACTION="READ", STATUS="OLD", IOSTAT=ios)
IF(ios /= 0) THEN
PRINT *, "ERROR, could not open file.", TRIM(filename), "Error code: ", ios
STOP
END IF
READ (UNIT=15, FMT=100) count
PRINT *, "Number of cities: ", count
!Allocate memory for all needed arrays
ALLOCATE(city_list(1:count), d_table(1:count,1:count), best_path(1:count), path(1:count), STAT=ios)
IF(ios /= 0) THEN
PRINT *, "ERROR, could not allocate memory."
STOP
END IF
!Fill in arrays from data file
!READ (UNIT=15, FMT=100) count
DO i=1, count
path(i-1) = i
READ (UNIT=15, FMT=200, IOSTAT=ios) city_list(i)
IF(ios < 0) THEN
EXIT
END IF
DO j=1, 4
print*,i,j,city_list(i)
READ (UNIT=15, FMT=100) d_table(i,j)
END DO
END DO
!Use recursion to find minimal distance
CALL permute(2, count)
!Print formatted output
PRINT *
DO i=1, count
PRINT *, path(i)
END DO
DO i=1, count
PRINT *, (city_list(i))
END DO
DO i=1, count
DO j=1, count
PRINT *, d_table(i,j)
END DO
END DO
100 FORMAT (I6)
200 FORMAT (A)
CONTAINS
!Permute function
RECURSIVE SUBROUTINE permute(first, last)
!Declare intent of parameter variables
IMPLICIT NONE
INTEGER, INTENT(in) :: first, last
INTEGER :: i, temp
IF(first == last) THEN
distance = d_table(1,path(2))
PRINT *, city_list(1)%name, city_list(path(2))%name, " ", d_table(1, path(2))
DO i=2, last-1
distance = distance + d_table(path(i),path(i+1))
print *, city_list(path(i))%name, " ", city_list(path(i+1))%name, d_table(path(i),path(i+1))
END DO
distance = distance + d_table(path(last),path(1))
PRINT *, city_list(path(last))%name," ",city_list(path(1))%name, d_table(path(last),path(1))
PRINT *, "Distance is ",distance
PRINT *
permutations = permutations + 1
IF(distance < best_distance) THEN
best_distance = distance
DO i=2, count
best_path(i) = path(i)
END DO
END IF
ELSE
DO i=first, last
temp = path(first)
path(first) = path(i)
path(i) = temp
call permute(first+1,last)
temp = path(first)
path(first) = path(i)
path(i) = temp
END DO
END IF
END SUBROUTINE permute
END PROGRAM P4