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NaN (not a number) is a numeric data type value representing an undefined or unrepresentable value. These values result from operations which have undefined numerical results. NaN is not the same as infinity.

1 program NotANumber(input, output, stderr);
2 begin
3 	// writes 'Nan' (with spacing) on its own line
4 	writeLn(0/0);
5 end.

Note, NaN exists only in the context of floating point number calculations: 0 div 0 (integer division) is not allowed, though.

See also