请看: https://so.csdn.net/so/search?q=c%E8%AF%AD%E8%A8%80ascii%E7%A0%81%E8%A1%A8&t=blog&u=&utm_term=c%E8%AF%AD%E8%A8%80ascii%E7%A0%81%E8%A1%A8&utm_medium=distribute.pc_toolbar_associateword.none-task-associate_word-opensearch_query-10-c%E8%AF%AD%E8%A8%80ascii%E7%A0%81%E8%A1%A8.nonecase&depth_1-utm_source=distribute.pc_toolbar_associateword.none-task-associate_word-opensearch_query-10-c%E8%AF%AD%E8%A8%80ascii%E7%A0%81%E8%A1%A8.nonecase&request_id=162639829716780357294041&opensearch_request_id=162639829716780357294041
查一下 ASCII 表, C 语言字符处理。