Switch c string Clearance

Product Name: Switch c string Clearance
I'm trying to make a program to switch letter cases, from lower case to upper case and vice versus, but I can't get it to run through the first if statement, any Clearance, cttrie - Compile time TRIE based string matching Clearance, determining a string inside a switch in C - It_qna Clearance, I'm trying to make a program to switch letter cases, from lower case to upper case and vice versus, but I can't get it to run through the first if statement, any Clearance, 馬克: C# 學習筆記part 12 教你使用switch case 匹配，範例在DOS 模式執行 Clearance.