if从句练习题和答案
if引导的从句有哪些？
if引导的从句有哪些？
if当如果引导条件状语从句。
if的用法：表示条件，意思是如果；表示虚拟，意思是假如；表示是否的含义，和whether相同用法，连接宾语从句。 扩展资料
1.(表示条件)如果 ,主句用将来时,if从句用现在时表示将来
He will come if you invite him.
如果你请他,他会来的.
2.(表示虚拟)假如,要是
时态：可以表示过去,现在和将来的情况.它的`基本特点是时态退后.
a.同现在事实相反的假设.
句型 ：条件从句主句
一般过去时 should( would) 动词原形
If they were here,they would help you.
b.表示于过去事实相反的假设.
句型：条件从句主句
过去完成时 should(would) have 过去分词
If she had worked harder,she would have succeeded.
The rice would not have been burnt if you had been more careful.
If my lawyer had been here last Saturday,he would have prevented me from going.
If he had come yesterday,I should / would have told him about it.
含义：He did not come yesterday,so I did not tell him about it.
If he had not been ill and missed many classes,he would have made greater progress.
含义：He was ill and missed many lessons,so he did not make greater progress.
c.表示对将来的假想
句型：条件从句主句
一般过去时 should 动词原形
were 不定式 would 动词原形
should 动词原形
If you succeeded,everything would be all right.
If you should succeed,everything would be all right.
If you were to succeed,everything would be all right.
3.是否 whether 连接宾语从句
I wonder if she is ill.
不知她是否病了.
if语句语法正确的是？
A.if(x＞0) printf(“%f”,x) 这里少分号 else printf(“%f”,-x);
B.if(x＞0) ｛xx y; printf(“%f”,x);｝ else printf(“%f”,-x); 正确
C.if(x＞0) ｛xx y; printf(“%f”,x);｝; 这里多分号 else printf(“%f”,-x) 这里少分号
D.if(x＞0) ｛xx y; printf(“%f”,x) 这里少分号 ｝ else printf(“%f”,-x);