It happens so often, I’m curious as to why the C language standard I\/O header file doesn’t define TRUE and FALSE. Then again, what is TRUE and FALSE to a programming language — or to a computer? Why is this value true and that value false in the first place?
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\nThe C language treats any non-zero value as a logical TRUE. The value zero is FALSE.<\/p>\n
Yes, even negative values are TRUE. This concept throws me. Once upon a time, I must have worked in a programming language where -1 was FALSE. That’s not the case in C, as the following code demonstrates.<\/p>\n
\r\n#include <stdio.h>\r\n\r\nint main()\r\n{\r\n int tf;\r\n\r\n for(tf=-5;tf<=5;tf++)\r\n {\r\n if(tf)\r\n printf(\"%d is TRUE\\n\",tf);\r\n else\r\n printf(\"%d is FALSE\\n\",tf);\r\n }\r\n\r\n return(0);\r\n}<\/pre>\nHere’s sample output:<\/p>\n
-5 is TRUE\r\n-4 is TRUE\r\n-3 is TRUE\r\n-2 is TRUE\r\n-1 is TRUE\r\n0 is FALSE\r\n1 is TRUE\r\n2 is TRUE\r\n3 is TRUE\r\n4 is TRUE\r\n5 is TRUE<\/code><\/pre>\nI could have extended the range for variable tf<\/code> to the entire int<\/em> spectrum. The output would be similar, with millions of TRUE values and only one FALSE value, zero.<\/p>\nThe advantage of this arrangement is that you can use a single value as a condition in an if<\/em> statement or while<\/em> loop, or anywhere a comparison is required. Non-zero values evaluate to TRUE.<\/p>\nIf you’re going to declare TRUE and FALSE constants in your code, do it this way:<\/p>\n
#define FALSE 0\r\n#define TRUE !FALSE<\/code><\/pre>\nFALSE<\/code> is always zero. TRUE<\/code> is any value that is “not” zero, or !FALSE<\/code>. If you define TRUE as equal to 1, then you can mess up some conditions elsewhere in the code where a value other than 1 is legitimately considered to be TRUE.<\/p>\n","protected":false},"excerpt":{"rendered":"Most values are considered TRUE; only one value is FALSE. Continue reading