# Do

Do[expr,n]

evaluates expr n times.

Do[expr,{i,imax}]

evaluates expr with the variable i successively taking on the values 1 through imax (in steps of 1).

Do[expr,{i,imin,imax}]

starts with i=imin.

Do[expr,{i,imin,imax,di}]

uses steps di.

Do[expr,{i,{i1,i2,}}]

uses the successive values i1, i2, .

Do[expr,{i,imin,imax},{j,jmin,jmax},]

evaluates expr looping over different values of j etc. for each i.

# Details

• Do uses the standard Wolfram Language iteration specification.
• You can use Return, Break, Continue, and Throw inside Do.
• Unless an explicit Return is used, the value returned by Do is Null.
• Do[expr,Infinity] continues evaluating expr until explicitly told to exit through a function such as Break, Return, Throw, Abort, or Quit.
• Do[expr,spec] first evaluates spec, then localizes the variable specified and successively assigns values to it, each time evaluating expr.
• Do effectively uses Block to localize values or variables.
• Do[expr,spec1,spec2] is effectively equivalent to Do[Do[expr,spec2],spec1].

# Examples

open allclose all

## Basic Examples(3)

Print the first four squares:

n goes from -3 to 5 in steps of 2:

Print 4 random integers:

## Scope(8)

Evaluate Print[x] twice:

The step can be negative:

The values can be symbolic:

Loop over i and j, with j running up to i-1:

The body can be a procedure:

Break breaks out of Do:

Continue continues the loop, without executing the rest of the body:

Loop infinitely, until a condition is met:

## Generalizations & Extensions(1)

Give a list of values to iterate over:

## Applications(5)

Generate a symbolic continued fraction:

Build up a list of primes:

Alternatively use Reap and Sow:

Implement backsubstitution:

Implement LU triangular decomposition of matrices:

The selection sort algorithm:

## Properties & Relations(2)

Equivalent loops:

Loop infinitely, until a condition is met:

Wolfram Research (1988), Do, Wolfram Language function, https://reference.wolfram.com/language/ref/Do.html (updated 2015).

#### Text

Wolfram Research (1988), Do, Wolfram Language function, https://reference.wolfram.com/language/ref/Do.html (updated 2015).

#### BibTeX

@misc{reference.wolfram_2021_do, author="Wolfram Research", title="{Do}", year="2015", howpublished="\url{https://reference.wolfram.com/language/ref/Do.html}", note=[Accessed: 21-June-2021 ]}

#### BibLaTeX

@online{reference.wolfram_2021_do, organization={Wolfram Research}, title={Do}, year={2015}, url={https://reference.wolfram.com/language/ref/Do.html}, note=[Accessed: 21-June-2021 ]}

#### CMS

Wolfram Language. 1988. "Do." Wolfram Language & System Documentation Center. Wolfram Research. Last Modified 2015. https://reference.wolfram.com/language/ref/Do.html.

#### APA

Wolfram Language. (1988). Do. Wolfram Language & System Documentation Center. Retrieved from https://reference.wolfram.com/language/ref/Do.html