出现“分段故障（核心转储）”消息

when running this program, it prints to the screen "Please enter a character: " and allows me to input a character 4 times. After that nothing happens, and when I hit enter, the message "Segmentation fault (core dumped)" comes up and I'm not sure why. If anyone could help that would be great, thanks!when running this program, it prints to the scr