Batch edit

Calculation

Batch scripts can do simple 32-bit integer arithmetic and bitwise manipulation using SET /a command. The largest supported integer is 2147483647 = 2 ^ 31 - 1. The smallest supported integer is -2147483648 = - (2 ^ 31), assignable with the trick of set /a num=-2147483647-1. The syntax is reminiscent of the C language.

Arithmetic operators include *, /, % (modulo), +, -. In a batch, modulo has to be entered as "%%".

Bitwise operators interpret the number as a sequence of 32 binary digits. These are ~ (complement), & (and), | (or), ^ (xor), << (left shift), >> (right shift).

A logical operator of negation is !: it turns zero into one and non-zero into zero.

A combination operator is ,: it allows more calculations in one set command.

Combined assignment operators are modeled on "+=", which, in "a+=b", means "a=a+b". Thus, "a-=b" means "a=a-b". Similarly for *=, /=, %=, &=, ^=, |=, <<=, and >>=.

The precedence order of supported operators, is as follows:

  1. ( )
  2. * / % + -
  3. << >>
  4. &
  5. ^
  6. |
  7. = *= /= %= += -= &= ^= |= <<= >>=
  8. ,

Literals can be entered as decimal (1234), hexadecimal (0xffff, leading 0x), and octal (0777, leading 0).

The internal bit representation of negative numbers is two's complement. This provides a connection between arithmetic operations and bit operations. For instance, -2147483648 is represented as 0x80000000, and therefore set /a num=~(-2147483647-1) yields 2147483647, which equals 0x7FFFFFFF (type set /a num=0x7FFFFFFF to check).

As some of the operators have special meaning for the command interpreter, an expression using them needs to be enclosed in quotation marks, such as this:

Examples:

An example calculation that prints prime numbers:

@echo off
setlocal
set n=1
:print_primes_loop
set /a n=n+1
set cand_divisor=1
:print_primes_loop2
set /a cand_divisor=cand_divisor+1
set /a cand_divisor_squared=cand_divisor*cand_divisor
if %cand_divisor_squared% gtr %n% echo Prime %n% & goto :print_primes_loop
set /a modulo=n%%cand_divisor
if %modulo% equ 0 goto :print_primes_loop & REM Not a prime
goto :print_primes_loop2

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