https://community.intel.com/t5/Software-Archive/checking-for-NaN/m-p/945979#M18290 I have a program that sometimes generates a NaN value. I want to check for this in order to react to it, and I was trying to use the test 'if (A /= A) then' . . . <BR />I tried this first in an interactive program that compiles as a QuickWin Application, and it worked just fine - when A = NaN the if condition evaluated to true. <BR />But then when I switched to a batch program that compiles as a Fortran Console Application, it stopped working. No matter what the value of A, the if condition always evaluates to false. <BR />The compiler options on the two projects should be identical, including having optimization turned off. Can anyone tell me what the difference between the two is, and why I can't use this test in the Fortran Console Application project? Sat, 07 Apr 2001 05:57:22 GMT jltate 2001-04-07T05:57:22Z https://community.intel.com/t5/Software-Archive/checking-for-NaN/m-p/945979#M18290 I have a program that sometimes generates a NaN value. I want to check for this in order to react to it, and I was trying to use the test 'if (A /= A) then' . . . <BR />I tried this first in an interactive program that compiles as a QuickWin Application, and it worked just fine - when A = NaN the if condition evaluated to true. <BR />But then when I switched to a batch program that compiles as a Fortran Console Application, it stopped working. No matter what the value of A, the if condition always evaluates to false. <BR />The compiler options on the two projects should be identical, including having optimization turned off. Can anyone tell me what the difference between the two is, and why I can't use this test in the Fortran Console Application project? Sat, 07 Apr 2001 05:57:22 GMT https://community.intel.com/t5/Software-Archive/checking-for-NaN/m-p/945979#M18290 jltate 2001-04-07T05:57:22Z https://community.intel.com/t5/Software-Archive/checking-for-NaN/m-p/945980#M18291 According to the IEEE spec, a NaN is supposed to compare as "not equal" to everything, including another NaN. I know we've fixed some problems in this regard in more recent versions.<BR /><BR />You want to use the ISNAN intrinsic instead.<BR /><BR />Steve Sat, 07 Apr 2001 10:24:34 GMT https://community.intel.com/t5/Software-Archive/checking-for-NaN/m-p/945980#M18291 Steven_L_Intel1 2001-04-07T10:24:34Z