The ornamental design for a monitor for computer, as shown and described.
1. Monitor for computer
1.1 : Perspective
1.2 : Rear perspective view
1.3 : Front
1.4 : Back
1.5 : Left
1.6 : Right
1.7 : Top
1.8 : Bottom
1.9 : Reference
1.10 : Reference
The broken lines indicate portions of the article that form no part of the claimed design; reproductions 1.9 and 1.10 are reference views showing the display part is lowered and the display part is rotated, respectively.