Linear Search [CPP]

[Proder]

<!- Hi! Thanks for considering contributing to this ever-growing list of algorithm and data structure implementations. Your contribution is valuable. In order to help us evaluate PRs better, we ask you to have a look at the following declaration and check the points you agree with. ( [x] ) PRs which don't agree to all the points mentioned below will be rejected. Also make sure that this PR corresponds to one and only one issue. Write the issue number in the space provided below. -->

Fixes #834

By submitting this pull request I confirm I've read and complied with the below declarations.

• [X] I have read the Contribution guidelines and I am confident that my PR reflects them.
• [X] I have followed the coding guidelines for this project.
• [X] My code follows the skeleton code structure.
• [X] This pull request has a descriptive title. For example, Added {Algorithm/DS name} [{Language}], not Update README.md or Added new code.
• [X] This pull request will be closed if I fail to update it even once in a continuous time span of 7 days.
• [X] This pull request shall only be reviewed and merged once the Travis build passes. No maintainer or supporter shall be obliged to review it before this condition is met.
• [X] I have mentioned the issue number correctly (with hyperlink) in this pull request description.