Atoi

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The correct title of this article is atoi. The initial letter is shown capitalized due to technical restrictions.

The atoi function in the C programming language is used to convert a string into a numerical representation.

int atoi (const char *string)

Where string is the string, represented by an array of characters. When atoi encounters a string with no numerical sequence, it returns a 0 (zero). Also, if the string holds a valid sequence of digits that represents the number 0, it would also return a 0, making it impossible to tell from the return value alone whether the string held a valid number of not. The newer function strtol does not have this deficiency.

Variants of the atoi function, atol and atoll (the latter formerly known as atoq), are used to convert a string into a long or long long integer, respectively:

long atol (const char *string)

long long atoll (const char *string)