Integers

Integers are just whole numbers. They’re kind of the main data type used in C!

In fact, when C was just beginning, pretty much everything was an integer, or made out of integers.

Syntax

Integers have the type int.

We can declare an int variable like this:

int myInteger;

We can also assign a value to it:

myInteger = 42;

Or we can do both at the same time:

int myInteger = 42;

Size of integers

Integers are usually 4 bytes (32 bits) in size on modern systems, but this can vary depending on the architecture and compiler - because… C.

If we assume integers are 4 bytes:

• The smallest integer we can represent is -2,147,483,648 (which is -2^31)
• The largest integer we can represent is 2,147,483,647 (which is 2^31 - 1)
• Or, in other words, we can represent integers from -2.1 billion to +2.1 billion.
• We can represent a total of 2^{32} different integer values (about 4.2 billion)

That’s usually enough, but we also have other integer types if we need more or less range. We’ll cover those later.

Integer constants

We’ve seen an integer constant already - 42.

A constant is any value in our program that doesn’t change. Here, 42 is a hardcoded value and doesn’t change depending on input to the program or anything else.

To use an integer constant, we just write it out in our code! Here’s some examples:

int a = 10;
int b = 0;
int c = -5;

Operations on integers

THere are lots of operations we can do to integer variables. For example:

• Addition: +
• subtraction: -
• multiplication: *
• division: /
• modulus (remainder): %
• Increment: ++
• Decrement: --
• Bitwise AND: &
• Bitwise OR: |
• Bitwise XOR: ^
• Bitwise NOT: ~
• Left shift: <<
• Right shift: >>

…and more!

Here’s an example of some integer operations:

int a = 10;
int b = 3;
int sum = a + b;          // sum is 13
int difference = a - b;   // difference is 7
int product = a * b;      // product is 30
int quotient = a / b;     // quotient is 3
int remainder = a % b;    // remainder is 1
a++;                       // a is now 11
b--;                       // b is now 2
int andResult = a & b;    // andResult is 2
int orResult = a | b;     // orResult is 11
int xorResult = a ^ b;    // xorResult is 9
int notResult = ~a;       // notResult is -12
int leftShift = a << 1;   // leftShift is 22
int rightShift = a >> 1;  // rightShift is 5