Looks like the UNC-CH admission process for the CS major is non-transparent and holistic:
https://cs.unc.edu/undergraduate/cs-admissions/
NCSU CS also requires secondary admission after entering as an engineering first year student:Join a Department – Change of Degree Application (CODA) | College of Engineering
If CS is a must, direct admission to the CS major at Purdue is valuable over needing to go through secondary admission with unknown selectivity. If you highly value the certainty of major and can afford Purdue without debt, then Purdue becomes an attractive choice.