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List of Some Commonly used inbuilt Functions in C++

Standard input/output functions

stdio.h

gets (), puts ()

Character Functions

ctype.h

isalnum (), isalpha (),isdigit (), islower (),isupper (), tolower (),toupper ()

String Functions

string.h

strcpy (), strcat (),strlen (), strcmp (),strcmpi (), strrev (),strlen (), strupr (),strlwr ()

iomanip.h

setw(),

Mathematical Functions

math.h

abs (), pow (), sgrt (),sin (), cos (), abs ()

Other Functions

stdlib.h

randomize (), random (),itoa (), atoi ()

Using Library Functions

Header File :ctype.h

int isalnum(int c);

Description:

The function returns nonzero if c is any of:

a b c d e f g h i j k l m n o p q r s t u v w x y z
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
o 1 2 3 4 5 6 7 8 9

Return Value

The function returns nonzero if c is alphanumeric otherwise this will return zero which will be equivalent to false.

Example

#include <iostream.h>
#include<ctype.h>
int main() {
  if( isalnum( '#' ) )
  {
     cout<< "Character # is not alphanumeric\n" ;
  }
  if( isalnum( 'A' ) )
  {
     cout<< "Character A is alphanumeric\n" ;
  }
  return 0;
}
It will produce following result:
Character A is alphanumeric

int isalpha(int c);

Description:

The function returns nonzero if c is any of:

a b c d e f g h i j k l m n o p q r s t u v w x y z
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

Return Value

The function returns nonzero if c is just alpha otherwise this will return zero which will be equivalent to false.

Example

#include <iostream.h>
#include<ctype.h>
int main() {
  if( isalpha( '1' ) )
  {
     cout<< "Character 1 is not alpha\n" ;
  }
  if( isalpha( 'A' ) )
  {
     cout<< "Character A is alpha\n";
  }
  return 0;
}
It will produce following result:
Character A is alpha

int isdigit(int c);

Description:

The function returns nonzero if c is any of:

0 1 2 3 4 5 6 7 8 9

Return Value

The function returns nonzero if c is a digit otherwise this will return zero which will be equivalent to false.

Example

#include <iostream.h>
#include<ctype.h>
int main() {
  if( isdigit( '1' ) )
  {
     cout<< "Character 1 is a digit\n" ;
  }
  if( isdigit( 'A' ) )
  {
     cout<< "Character A is digit\n" ;
  }
  return 0;
}
It will produce following result:
Character 1 is a digit

int islower(int c);

Description:

The function returns nonzero if c is any of:

a b c d e f g h i j k l m n o p q r s t u v w x y z

Return Value

The function returns nonzero if c is lower case otherwise this will return zero which will be equivalent to false.

Example

#include <iostream.h>
#include<ctype.h>
int main() {
  if( islower( 'a' ) )
  {
     cout<<"Character a is lower case\n";
  }
  if( islower( 'A' ) )
  {
     cout<< "Character A is lower case\n";
  }
  return 0;
}
It will produce following result:
Character a is lower case

int isupper(int c);

Description:

The function returns nonzero if c is any of:

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

Return Value

The function returns nonzero if c is upper case otherwise this will return zero which will be equivalent to false.

Example

#include <iostream.h>
#include<ctype.h>
int main() {
  if( isupper( 'a' ) )
  {
     cout<< "Character a is upper case\n" ;
  }
  if( isupper( 'A' ) )
  {
     cout<<"Character A is upper case\n";
  }
  return 0;
}
It will produce following result:
Character A is upper case

int tolower(int c);

Description:

The function returns the corresponding lowercase letter.
Example

#include <iostream.h>
#include<ctype.h>
int main() {
  cout<< "Lower case of T is \n"<<tolower('T');
  return 0;
}
It will produce following result:
Lower case of T is t

int toupper(int c);

Description:

The function returns the corresponding uppercase letter.

Example

#include <iostream.h>
#include<ctype.h>
int main() {
  cout<< "Upper case of t is \n"<<toupper('t');
  return 0;
}
It will produce following result:
Upper case of t is T

C++ Library Functions Header File :string.h

char *strcpy (char *dest, char *src);

Description:
The strcpy function copies characters from src to dest including the terminating null character.
Return Value

The strcpy function returns dest.

Example
#include <iostream.h>

#include <string.h>

int main() {

  char src[20];

  char dest[20];

  strcpy(src, "Hello");

 strcpy(dest, src");

// Will copy the contents from src array to dest array

  cout<<"dest ="<<dest;

  return 0;

}
It will produce following result:

dest = Hello

char *strcat(char *dest, const char *src);

Description:
The strcat function concatenates or appends src to dest. All characters from src are copied including the terminating null character.

Return Value

The strcat function returns dest. Example

#include <string.h>

#include <iostream.h>

int main()

{
  char src[20];

  char dest[20];

  strcpy(src, "Ayan");

  strcpy(dest, "Sharma");

  cout<<"Concatenated String =  \n"<<strcat(src,dest);

  return 0;

}
It will produce following result:

Concatenated String = AyanSharma

int strlen(char *src );

Description:
The strlen function calculates the length, in bytes, of src. This calculation does not include the null terminating character.


Example
#include <string.h>

#include <iostream.h>

int main()

{
  char src[20];

  strcpy(src, "Ambari");

cout<<"Length of string :"<<src<< " is "<<strlen(src );

  return 0;


}
It will proiduce following result:

Length of string Ambari is  6

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int strcmp(char *string1, char *string2); 

Description:
The strcmp function compares the contents of string1 and string2 and returns a value indicating their relationship.
Return Value

if Return value if < 0 then it indicates string1 is less than string2

if Return value if > 0 then it indicates string2 is less than string1

if Return value if = 0 then it indicates string1 is equal to string1

Example
#include <string.h>

#include <iostream.h>

int main()

{
  char one[20];

  char two[20];

  strcpy(one, "Ayan");

  strcpy(two, "Sharma");

  cout<<"Return Value is : \n"<<strcmp( one, two);

  strcpy(one, "Sharma");

  strcpy(two, "Ayan");

  cout<<"Return Value is : \n"<<strcmp( one, two);

  strcpy(one, "Ayan");

  strcpy(two, "Ayan");

  cout<<"Return Value is : \n"<<strcmp( one, two);

  return 0;

}
It will produce following result:

Return Value is : -18

Return Value is : 18

Return Value is : 0

Declaration: char *strupr(char *s);

Description:

strupr  convert lowercase letters (a to z) in string s to uppercase (A to Z).

#include <iostream.h>
#include <string.h>

 int main(void)
 {
    char *s = "abcde";

    /* converts string to upper case characters */
    cout<<endl<<s;
    return 0;
 }

Output

ABCDE

Declaration: char *strrev(char *s);

Description:

strrev  changes all characters in a string to reverse order, except the terminating null character.For example, it would change
  AYAN\0
to
  NAYA\0

#include<string.h>
#include<iostream.h>

 int main(void)
 {
    char *s = "AYAN";

    cout<<"After strrev():  "<<strrev(s);
    return 0;
 }

Output

NAYA

C++ Library Functions Header File :math.h

Declaration :- abs(int n);

 Description:

abs is not a function but is a macro and is used for calculating absolute value of a number.

#include <iostream.h>

#include <math.h>

 int main()

{
  int n, result;

cout<<"Enter an integer to calculate it's absolute value\n";
  cin>>n;

  result = abs(n);

  cout<<"Absolute value of "<<n<< "is "<<result;

  return 0;

Output

Enter an integer to calculate it's absolute value  -5

Absolute value of  -5 is 5

Declaration :- double pow(double, double);

Description:

pow function returns x raise to the power y where x and y are variables of double data type.

#include <iostream.h>

#include <math.h>

 int main()

{
  int m,n, result;

  cout<<"Enter two integers to calculate power\n";

  cin>>m>>n;

  result = pow(m,n);

  cout<<"Result is "<<result;

  return 0;

}

Output

Enter two integers to calculate power 3 4

Result is 81

Declaration :- double sqrt(double);

Description:

sqrt function returns square root of a number.

#include <iostream.h>

#include <math.h>

 int main()

{
  double n, result;

cout<<"Enter an integer to calculate it's square root \n";

  cin>>n;

  result = sqrt(n);

 cout<<"Result is "<<result;

  return 0;

}

Output

Enter an integer to calculate it's square root 9

Result is 3

Declaration: double sin(double);

Description:

Sin function returns sine of an angle(in radian).

#include <iostream.h>

#include <math.h>

 int main()

{
  double result, x = 0.5;

   result = sin(x);

   cout<<"sin(x ) of 0.5  is "<<result;

  return 0;

}

Output

sin(x) of 0.5 is 0.479426

Declaration: double cos(double);

Description:

Cos function returns cosine of an angle(in radian).
1 radian = 57.2958(approximately).

#include <iostream.h>

#include <math.h>

 int main()

{
  double result, x = 0.5;

   result = cos(x);

   cout<<"cos(x) of 0.5 is  "<<result;

  return 0;

}

Output

cos(x) of 0.5 is 0.877583

C++ Library Functions Header File :stdlib.h

Declaration: int random(int n);

Description:

random return a random number between 0 to (n-1)
#include <stdlib.h>

#include <iostream.h>

#include <time.h>

 /* prints a random number in the range 0 to 9 */

 int main(void)

 {
  randomize();

cout<<"Random number from 0-9 range:\n"<<random(10);
  return 0;


 }

Declaration: void randomize(void);

Description:

randomize initializes random number generator
#include <stdlib.h>

#include <iostream.h>

#include <time.h>

 /* prints 3 random number in the range 0 to 9 */

 int main(void)

 {
  randomize();

  cout<<"3 random numbers from 0-9 range:\n";

  for(int i=0;i<3;i++)

  cout<<random (10)<<endl;

  return 0;

 }

Declaration:

char*itoa(int value,char *string,int radix);

Description: itoa converts an integer to a string

#include <iostream.h>
#include <stdlib.h>

 int main(void)
 {
    int number = 444;
    char string[5];

    itoa(number, string, 10);
    cout<<"integer = "<<number<<"string ="<<string;
    return 0;
 }

Output

integer 444 string 444

Declaration:  int atoi(const char *s);

Description: Macro that converts string to integer

#include <stdlib.h>
 #include <iostream.h>

 int main(void)
 {
    int n;
    char *str = "112";

    n = atoi(str);
    cout<<"string = "<<str<<"integer ="<<n;
    return 0;
 }

Output

string 112 integer 112

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