Source Code : Decision Statement ,Array Structure and Pointers In C++

Decision Statement ,Array Structure and Pointers In C++

if (condition) 

{

  stmt 1;  //Executes if Condition is true

}

else

{

  stmt 2;  //Executes if condition is false

}

switch(var) 

{

case 1:  //if var=1 this case executes

  stmt;

  break;

case 2:  //if var=2 this case executes

  stmt;

  break;

default:  //if var is something else this will execute

  stmt;

}

Strings

C++ provides following two types of string representations:

· The C-style character string.

· The string class type introduced with Standard C++.

The C-Style Character String:

The C-style character string originated within the C language and continues to be supported within C++. This string is actually a one-dimensional array of characters which is terminated by a nullcharacter '\0'. Thus a null-terminated string contains the characters that comprise the string followed by a null.

The following declaration and initialization create a string consisting of the word "Hello". To hold the null character at the end of the array, the size of the character array containing the string is one more than the number of characters in the word "Hello."

char greeting[6] = {'H', 'e', 'l', 'l', 'o', '\0'};

If you follow the rule of array initialization, then you can write the above statement as follows:

char greeting[] = "Hello";

String functions

strlen(str) – To find length of string str

strrev(str) – Reverses the string str as rts

strcat(str1,str2) – Appends str2 to str1 and returns str1

strcpy(st1,st2) – copies the content of st2 to st1

strcmp(s1,s2) – Compares the two string s1 and s2

strcmpi(s1,s2) – Case insensitive comparison of strings

Arrays

•Arrays fall under aggregate data type

•Aggregate – More than 1

•Arrays are collection of data that belong to same data type

•Arrays are collection of homogeneous data

•Array elements can be accessed by its position in the array called as index

•Array index starts with zero

•The last index in an array is num – 1 where num is the no of elements in a array

•int a[5] is an array that stores 5 integers

•a[0] is the first element where as a[4] is the fifth element

•We can also have arrays with more than one dimension

•float a[5][5] is a two dimensional array. It can store 5x5 = 25 floating point numbers

•The bounds are a[0][0] to a[4][4]

Structures

•Structures are user defined data types

•It is a collection of heterogeneous data

•It can have integer, float, double or character data in it

•We can also have array of structures

struct <>

{

  members;

}element;

We can access element.members;

struct Person

{

int id;

char name[5];

}P1;

P1.id = 1;

P1.name = “vasu�;

Pointers

Pointer is a special variable that stores address of another variable

Addresses are integers. Hence pointer stores integer data

Size of pointer = size of int

Pointer that stores address of integer variable is called as integer pointer and is declared as int *ip;

Pointers that store address of a double, char and float are called as double pointer, character pointer and float pointer respectively.

char *cp

float *fp

double *dp;

Assigning value to a pointer

int *ip = &a; //a is an int already declared

example:

#include

using namespace std;

int main ()

{

intvar = 20; // actual variable declaration.

int *ip; // pointer variable

ip = &var; // store address of var in pointer variable

cout << "Value of var variable: ";

cout << var << endl;

// print the address stored in ip pointer variable

cout << "Address stored in ip variable: ";

cout << ip << endl;

// access the value at the address available in pointer

cout << "Value of *ip variable: ";

cout << *ip << endl;

return 0;

}

C++ Pointers in Detail:

  Pointers have many but easy concepts and they are very important to C++ programming. There are following few important pointer concepts which should be clear to a C++ programmer:

Concept   Description  

C++ Null Pointers   C++ supports null pointer, which is a constant with a value   of zero

C++ pointer arithmetic   There are four arithmetic operators that can be used on   pointers: ++, --, +, -  

C++ pointers vs arrays   There is a close relationship between pointers and arrays.   Let us check how?  

C++ array of pointers   You can define arrays to hold a number of pointers.  

C++ pointer to pointer   C++ allows you to have pointer on a pointer and so on.  

  Passing pointers to functions   Passing an argument by   reference or by address both enable the passed argument   to be changed in the calling function by the called function 

Return pointer from functions C++ allows a function to return a pointer to local variable,  static variable and dynamically allocated memory as well.  

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