#include<iostream.h>
#include<stdio.h>
void main()
{
    struct STUDENT
      {
         char stu_name[20];
         char stu_sex;
         int stu_age;
     }student;
     gets(student.stu_name);
     cin>>(student.stu_sex);
}

A default parameter is a function parameter that has a default value provided to it. If the user does not supply a value for this parameter, the default value will be used.
If the user does supply a value for the default parameter, the user supplied value is used.
Consider the following program:
void Printvalues(int nValue1, int nValue2=10)
{
     cout<<"1st value:"<<nValue1<<endl;
     cout<<"2nd value:"<<nValue2<<endl;
}
int main()
{
    PrintValue(1);    
     //nValues2 will use default parameter
     //of 10
   PrintValues(3,4);
    //override default value for nValue2
    return 0;
}
Output
1st value:1
2nd value:10
1st value:3
2nd value:4

typedef keyword is used to assign alternative names to existing data types.
e.g. typedef int in;
Now, whenever we want to declare a variable of types integer, rather than using int, we can use 'in' keyword in place.
e.g. void main()
       {
          typedef int in;
                         //in is an alternative name to int 
          in a=10;
          cout<<a:  //a is of type integer
    }

The output is 5, 3, 4, 4 

An unsigned int can represent 0 to 65536 value in total, whereas a signed int can represent -32768 to 32767, i.e. 65536 values. The total numbers represented by both integers are the same but the range represented by unsigned int becomes double because in place of negative numbers positive values are represented thereby increasing the range by 32768 numbers as there are many negative values represented by signed int.

#include<iostream.h>
#include<conio.h>
struct students_record
{
    int s_rollno,s_class;
};
void display(struct students_record*s1);
void main()
{
     struct students_record s1;
     s1.s_rollno=14;
     s1.s_class=2;
     display(&s1);
     getch();
}
void display(struct students_record *s1)
{
   cout<<"\nRoll no: "<<s1->s_rollno;
   cout<<"\nClass:  "<<s1->s_class;
}
Output
Roll no:14
Class:2

The given program does not execute successfully because following errors are occurred during the execution:
#include<iostream.h>
          //required for cin and cout
#include<stdio.h>
voidmain()
{
int x, sum=0,n;
           //n should be declared before use
cin>>n;
            /*Here should be input operator  >>  in place of output operator<<*/
for( X=1;X<100; X+=2)
            /*Here should be(;) in place of(,) and x in place of x. */
if (X%2==0)
sum+=X;
          /* if expression should closed in brackets() and here, should be X in place of x*/
cout<<"sum="<<sum;
/*Here should be output operator << in place of input operator >>*/
}

#include<iostream.h>
#include<conio.h>
#include<process.h>
void main()
{
    int j;
    cout<<"Enter the bit value 0, 1 "<<"\n";
    cin>>j;
    switch(j)
    {
        case 0;
          cout<<"Bit value is 0"<<"\n";
           break;
       case 1;
          cout<<"Bit value is 1"<<"\n";
          break;
      default:
          exit(0);
   } 
    getch();
}
Output
Enter the bit value 0,1
0
Bit value is 0

#include<iostream.h>
#include<conio.h>
void main()
{
    int i, j;
    for(i=0; i<10; i++)
    {
          cout<<"\n Outer loop executing. i="<<i;        
           for(j=0; j<2; j++)
            {
                  cout<<"\n Inner loop executing. j="<<j;
                  if(i==3)
                       goto stop;
          }
    } 
 cout<<"\n Loop exited.  i="<<i;
stop;
                   //This message does not print 
 cout<<"\n Jumped to stop. i="<<i;
getch();
}
Output
Outer loop executing. i=0
Inner loop executing. j=0
Inner loop executing. j=1
Outer loop executing. i=1
Inner loop executing. j=0
Inner loop executing. j=1
Outer loop executing. i=2
Inner loop executing. j=0
Inner loop executing. j=1
Outer loop executing. i=3
Inner loop executing. j=0
Jumped to stop. i=3

#include
#include
void main()
{
      int count;
      for(count=0; count<11; count++)
           cout< 
getch();
}
Output
0 1 2 3 4 5 6 7 8 9 10
It is divided into three parts

#include<iostream.h>
void main()
{
       int code;
       code =1;
       if( code==1)
              cout<<" The water was too warm\n"
       else 
              cout<<" the water were all finished";
}
Output:
The water was too warm
Some of valid if-else statements are:
(i) If ((ch >= 'a') && (ch <= 'z'))
            cout<<ch<<" is a lowercase letter";
else
           cout<<ch<<" is not a lowercase letters";
(ii) if((age == 50) || (age >= 20))
             cout<<" You are old";
    else 
             cout<<" You are young";

#include<iostream.h>
void main()
{
        int a, b;
        a=10; b=20;
        if(a<b)
          cout<<"a is less than b";
}
Output
a is less than b

#include<iostream.h>
void main()
{
         int x, y, sum;
         cout<<" A program which adds two integers\n";
         cout<<"Enter 1st integer:";
         cin>>x;
         cout<<"Enter 2st integer:";
         cin>>y;
         sum = x+y;
         cout<<"sum is "<<sum
}
Output
A program which adds two integers
Enter the 1st integer: 20
Enter the 2nd integer: 25
Sum is 45

1*1=1
1*3=3
1*5=5
2*1=2
2*3=6
2*5=10
a=32
Now k=2, b=2, c=2.666667