Why Do Large Integer Literals in For Loops Behave Differently Than Expected?

Type of Integer Literals: Not Int by Default?

Question:

Why does a for loop iterating up to 10 billion take longer than one iterating up to 1 billion?

Answer:

The iteration variable in the loop is 32-bit and overflows, causing an infinite loop. The literal representing 10 billion, despite not having an L suffix, is automatically promoted to a fitting range (at least 64-bit in this case) by the compiler.

C :

According to the C 11 standard ([lex.icon] ¶2), the type of an integer literal without a suffix is the first one from Table 6 where its value can be represented:

Type

int

long int

long long int

Therefore, in this case, the literal is interpreted as a long int or long long int (if long int is 32-bit).

C:

In C99 ([§6.4.4.1]), the rule is similar. The type of an integer constant is determined by the first type from a similar list where its value can be represented.

Implementation-Defined Types:

Both C 11 ([lex.icon] ¶3) and C99 ([§6.4.4.1 ¶5]) allow integer literals to be of "extended integer types" (implementation-specific integer types) if no other valid type is found.

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