A strange result is obtained

[beam]

In the program below, a strange result is obtained (z = 6.013470016999178 E+153).
At the same time, no errors are issued when compiling and running the program?
program fpu
real(8) :: f, z
!***
f = 1.0d307
z = 's'*f
print *, f
print *, z
end program fpu

The contents of the file BuildLog.htm:
Build Log
Build started: Project: FPU1, Configuration: Release|x64
Output

Deleting intermediate files and output files for project 'FPU1', configuration 'Release|x64'.
Compiling with Intel(R) Visual Fortran Compiler 19.1.3.311 [Intel(R) 64]...
ifort /nologo /Od /fpe:0 /fp:strict /fp:except /fpconstant /assume:minus0 /Qfp-stack-check /Qfp-speculation=strict /module:"x64\Release\\" /object:"x64\Release\\" /Fd"x64\Release\vc150.pdb" /check:all /libs:static /threads /c /Qlocation,link,"C:\Program Files (x86)\Microsoft Visual Studio\2017\Enterprise\VC\Tools\MSVC\14.16.27023\bin\HostX64\x64" /Qm64 "C:\Users\chernov\source\repos\FPU1\FPU1\fpu.f90"
Linking...
Link /OUT:"x64\Release\FPU1.exe" /INCREMENTAL:NO /NOLOGO /MANIFEST /MANIFESTFILE:"x64\Release\FPU1.exe.intermediate.manifest" /MANIFESTUAC:"level='asInvoker' uiAccess='false'" /SUBSYSTEM:CONSOLE /IMPLIB:"C:\Users\chernov\source\repos\FPU1\FPU1\x64\Release\FPU1.lib" -qm64 "x64\Release\fpu.obj"
Embedding manifest...
mt.exe /nologo /outputresource:"C:\Users\chernov\source\repos\FPU1\FPU1\x64\Release\FPU1.exe;#1" /manifest "x64\Release\FPU1.exe.intermediate.manifest"

FPU1 - 0 error(s), 0 warning(s)

[Arjen_Markus]

This is apparently one of the extensions to the standard that the Intel compiler recognises. You can force an error message by using the option "-stand", so that this type of extensions is recognised and rejected.

[cryptogram]

I'd guess that this harks back to olden days when Fortran didn't have a native character type, but you could store character data in other types.

Adding a couple of lines reveals what is going on

f = 1.0d307
z = 's'*f
print *, f
print *, z
z = z/f
write(*,*) z
write(*,'(z16)') z

Write(*,*) z 

gets the real*8 equivalent of 's' which is

6.013470016999178E-154

printing  the same result in hex format you get
2020202020202073

which shows you that 's' consists of 7 blanks (hex code 20) followed by the hex code for lower case s.

The result of 's'*z is what you get if you take the bit pattern corresponding to an eight character string consisting of 7 blanks and 's', and, treating it like a real*8 number, multiply that by f

[mecej4]

You can avoid unwelcome surprises of this type by adding (or placing, as appropriate) the option /standard-semantics to the file ifort.cfg (in the same directory as the compiler driver, ifort.exe), or making a habit of selecting this option in the VS project configuration before building.

[Steve_Lionel · Accepted solution]

/stand (-std on Linux/Mac), not /standard-semantics. The first asks the compiler to warn of any non-standard usage (keeping in mind that there are some cases it won't catch). The second alters run-time behavior from defaults that conflict with the current standard.

[Ron_Green]

the option is

-stand

on Mac and Linux these days.  We are moving away from -std although it is still accepted