自制替换指定串函数

            function replacing(S,source,target:string):string;
            var site,StrLen:integer;
            begin
            {source在S中出现的位置}
            site:=pos(source,s);
            　
            {source的长度}
            StrLen:=length(source);
            {删除source字符串}
            delete(s,site,StrLen);
            {插入target字符串到S中}
            insert(target,s,site);
            {返回新串}
            replacing:=s;
            end;