CODEWITHSUNDEEP
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mingpepe
mingpepe

Reputation: 559

What is the default data type of number in C?

In C, 

unsigned int size = 1024*1024*1024*2;

which results a warning "integer overflow in expression..." While

unsigned int size = 2147483648;

results no warning?

Is the right value of the first expression is default as int? Where does it mention in C99 spec?

Upvotes: 15

Views: 5230

Answers (2)

2501
2501

Reputation: 25752

When using a decimal constant without any suffixes the type of the decimal constant is the first that can be represented, in order (the current C standard, 6.4.4 Constants p5):

  • int
  • long int
  • long long int

The type of the first expression is int, since every constant with the value 1024 and 2 can be represented as int. The computation of those constants will be done in type int, and the result will overflow.

Assuming INT_MAX equals 2147483647 and LONG_MAX is greater than 2147483647, the type of the second expression is long int, since this value cannot be represented as int, but can be as long int. If INT_MAX equals LONG_MAX equals 2147483647, then the type is long long int.

Upvotes: 19

ameyCU
ameyCU

Reputation: 16607

unsigned int size = 1024*1024*1024*2;

This expression 1024*1024*1024*2 (in the expression 1024 and 2 are of type signed int) produces result that is of type signed int and this value is too big for signed int . Therefore, you get the warning.

After that signed multiplication it is assigned to unsigned int .

Upvotes: 4

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