Swift -- 字符串首字母大写以及全部大小写转换

        //首字母大写
        let temSting1 = "wo xiao wo ku"
        print(temSting1.capitalized)
        Wo Xiao Wo Ku
        
        //全部转小写
        let temSting2 = "COMpletion"
        print(temSting2.lowercased())
        completion
        
        //全部转大写
        let temSting3 = "compleTION"
        print(temSting3.uppercased())
        COMPLETION
        
        //字符串d所包含字母个数，包括空格和其他
        let temSting4 = "comple TION"
        print(temSting3.underestimatedCount)
        11