The C Standard does not allow for implicit typing of variables and functions. The old C90 standard, which is no longer in force, C90 Standard did allow such implicit typing. ThereforeConseuently, there exists some legacy code that uses implicit typing. Some C compilers still support legacy code by allowing implicit typing, but it should not be used for new code. Because implicit declarations lead to less stringent type checking, they can often introduce unexpected and erroneous behavior or even security vulnerabilities.
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