"The applications for many colleges and universities allow students to specify an intended major, though this is not required – and not all students do so. In most cases, choosing to begin college as an undecided major or electing to declare a major before arriving on campus depends on an individual student’s situation.
Below are several scenarios for and against applying with an undecided major." …
From the article:
This can be a risky idea at some colleges where entering an engineering major from a non-engineering undeclared status can be highly competitive or difficult. The risk is that even a respectable frosh/soph GPA in major prerequisites (e.g. 3.0-3.2) may not be sufficient to enter the major, depending on the college. The student in this case may have to transfer to a different college or settle for some other major.
Of course, a student with weaker high school science and math performance may not be able to gain direct admission to the desired engineering major at a college with more competitive admissions. But such a student may be more likely to have trouble earning a competitive college GPA in college science and math courses than one with stronger high school science and math performance. But many colleges with less competitive admissions do offer engineering majors.
Here are some examples of the level of competition that may exist changing into an engineering major from a non-engineering undeclared status:
http://engineering.berkeley.edu/admissions/undergrad-admissions/change-college
https://www.engr.washington.edu/current/admissions/admitstats