So what constitutes a 64-bit signed integer? It helps to break down each word, starting from right to left. An integer is a whole number that does not include a decimal point. Examples include 1, 99, or 234536. "Signed" means the number can be either positive or negative, since it may be preceded by a minus (-) symbol. 64-bit means the number can store 263 or 18,446,744,073,709,551,616 different values (since one bit is used for the sign). Because the long data type is signed, the possible integers range from -9,223,372,036,854,775,808 to 9,223,372,036,854,775,807, including 0.
In modern programming languages, the standard integer (int) data type typically stores a 32-bit whole number. Therefore, if a variable or constant may potentially store a number larger than 2,147,483,647 (231 ÷ 2), it should be defined as a long instead of an int.
NOTE: In standard C, a long integer may be limited to a 32-bit value ranging from -2,147,483,648 to 2,147,483,647.