W3School TIY Editor

#include <stdio.h> #include <ctype.h> void checkNum(char c) { if (isalnum(c)) { printf("%c 是字母数字字符\n", c); } else { printf("%c 不是字母数字字符\n", c); } } int main() { char char1 = 'B'; char char2 = 'X'; char char3 = '+'; checkNum(char1); checkNum(char2); checkNum(char3); return 0; }