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

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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:

Introduced in 1988
 (1.0)
 |
Updated in 2014
 (10.0)
2015
 (10.2)