iscntrl() in C++ and its application to find control characters

In C++, iscntrl() is a predefined function used for string and character handling. cstring is the header file required for string functions and cctype is the headerfile required for character functions. A control character is one which is not a printable character i.e, it does not occupy a printing position on a display.

This function is used to check if the arguement contains any control characters. There are many types of control characters in C++ such as:

  • Horizontal tab – ‘\t’
  • Line feed – ‘\n’
  • Backspace – ‘\b’
  • Carriage return – ‘\r’
  • Form feed – ‘\f’
  • Escape

Syntax

int iscntrl ( int c ); 

Applications

  1. Given a string, we need to find the number of control characters in the string.

    Algorithm
    1. Traverse the given string character by character upto its length, check if character is a control character.
    2. If it is a control character, increment the counter by 1, else traverse to the next character.
    3. Print the value of the counter.

    Examples:

    Input : string='My name \n is \n Ayush'
    Output :2
    
    Input :string= 'This is written above \n This is written below'
    Output :1
    



    // CPP program to count control characters in a string
    #include <iostream>
    #include <cstring>
    #include <cctype>
    using namespace std;
       
    // function to calculate control characters
    void space(string& str)
    {
        int count = 0;
        int length = str.length();
        for (int i = 0; i < length; i++) {
            int c = str[i];
            if (iscntrl(c))
                count++;
        }
        cout << count;
    }
       
    // Driver Code
    int main()
    {
        string str = "My name \n is \n Ayush";
        space(str);
        return 0;

    Output:

    2
    
  2. Given a string, we need to print the string till a control character is found in the string.
    Algorithm
    1. Traverse the given string character by character and write the characters to the standard output using putchar().
    2. Break the loop when a control character is found in the string.
    3. Print the final string from the standard output.
    Examples:

    Input : string='My name is \n Ayush'
    Output :My name is
    
    Input :string= 'This is written above \n This is written below'
    Output :This is written above
    
    // CPP program to print a string until a control character
    #include <iostream>
    #include <cstring>
    #include <cctype>
    #include<cstdio>
    using namespace std;
      
    // function to print string until a control character
    int space(string& str)
    {
         int i=0;
      while (!iscntrl(str[i]))
      {
        putchar (str[i]);
        i++;
      }
      return 0;
    }
      
    // Driver Code
    int main()
    {
        string str = "My name is \n Ayush";
        space(str);
        return 0;
    }

    Output:

    My name is
    

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