C++ if-else语句

if(condition){  
  //要执行的代码
}

#include <iostream>
using namespace std;
 
int main () {
   int num = 10;  
   if (num % 2 == 0)  
   {  
       cout<<"It is even number";  
   } 
   return 0;
}

if(condition){  
  //条件为真时的代码
}else{  
  //条件为假时的代码
}  

#include <iostream>
using namespace std;
int main () {
   int num = 11;  
   if (num % 2 == 0)  
   {  
      cout<<"It is even number";  
   } 
   else
   {  
      cout<<"It is odd number";  
   }
   return 0;
}

#include 
using namespace std;
int main () {
    int num;
    cout<<"Enter a Number: ";
    cin>>num;
    if (num % 2 == 0)  
    {  
        cout<<"It is even number"<<endl;  
    } 
    else
    {  
        cout<<"It is odd number"<<endl;  
    }
   return 0;
}

if(condition1){  
  //条件1为真时执行的代码
}else if(condition2){  
  //条件2为真时执行的代码 
}  
else if(condition3){  
  //条件3为真时执行的代码
}  
...  
else{  
  //如果所有条件都为假，则要执行的代码 
}  

#include <iostream>
using namespace std;
int main () {
       int num;
       cout<<"Enter a number to check grade:";  
       cin>>num;
            if (num 100)  
            {  
                cout<<"wrong number";  
            }  
            else if(num >= 0 && num < 50){  
                cout<<"Fail";  
            }  
            else if (num >= 50 && num < 60)  
            {  
                cout<<"D Grade";  
            }  
            else if (num >= 60 && num < 70)  
            {  
                cout<<"C Grade";  
            }  
            else if (num >= 70 && num < 80)  
            {  
                cout<<"B Grade";  
            }  
            else if (num >= 80 && num < 90)  
            {  
                cout<<"A Grade";  
            }  
            else if (num >= 90 && num <= 100)  
            {  
                cout<<"A+ Grade";
            }  
    }