1.string s1="I"; s1+="love you"; s1+='!'; string s2="love girl"; s1+=s2; 2.string s3="You"; s3.append("love"); s3.append("girl love",4);//前四个加到尾部 s3.append(s2); s3.append(s2,0,4); 截取一段加到后面