分支结构
1,if语句
ch2_7.cpp
//计算a+|b|的值 #include<iostream> using namespace std; int main(){ int a,b,c; cout<<"请输入a,b的值"<<endl; cin>>a>>b; if(b<0){ c = a-b; } else{ c = a+b; } cout<<"a+|b|="<<c<<endl; return 0; }
ch2_8.cpp
//求一元二次方程的根 #include<iostream> #include<cmath> using namespace std; int main(){ int a,b,c; double x1,x2,disc; cout<<"请输入一元二次方程的系数:"<<endl; cin>>a>>b>>c; if(a==0){ cout<<"方程不是一元二次方程"<<endl; } else{ disc = b*b-4*a*c; if(disc==0){ x1=x2=-b/2*a; cout<<"x1=x2="<<-b/2*a<<endl; } else{ if(disc>0){ x1 = (-b+sqrt(disc))/(2*a); x1 = (-b-sqrt(disc))/(2*a); cout<<"方程的两个不同的根为:"<<x1<<"and"<<x2<<endl; } else{ cout<<"方程没有实根"<<endl; } } } return 0; }
2,switch语句
switch语句语法:
switch(){
case 标号1:语句1;break;
case 标号2:语句2;break;
...
case 标号n:语句n;break;
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default:语句n+1;
}
ch2_9.cpp
//判断元音字符 #include<iostream> using namespace std; int main(){ char c; cout<<"请输入字符c"<<endl; cin>>c; switch(c){ case 'a': case 'e': case 'i': case 'o': case 'u': cout<<"小写元音字母"<<endl; break; case 'A': case 'E': case 'I': case 'O': case 'U': cout<<"大写元音字母"<<endl; default: cout<<"其他字符"<<endl; } return 0; }
循环结构
1,while循环
ch1_10.cpp
//使用while计算1-100的值 #include<iostream> using namespace std; int main(){ int sum = 0; int i = 1; while(i<=100){ sum = sum+i; i++; } cout<<"1-100的和为:"<<sum<<endl; return 0; }
2,do-while循环
//使用do-while计算1-100的值 #include<iostream> using namespace std; int main(){ int sum = 0; int i = 1; do{ sum = sum+i; i++; }while(i<=100); cout<<"1-100的和为:"<<sum<<endl; return 0; }
3,for循环
//使用for计算1-100的值 #include<iostream> using namespace std; int main(){ int sum = 0; int i ; for(i=1;i<=100;i++){ sum =sum + i; } cout<<"1-100的和为:"<<sum<<endl; return 0; }