Skill summary

ACM skills summary

1. Substr function
substr() of string-interception of string

    string s = "0123456789";
    string sub1 = s.substr(5); //只有一个数字5表示从下标为5开始一直到结尾：sub1 = "56789"
    string sub2 = s.substr(5, 3); //从下标为5开始截取长度为3位：sub2 = "567"