Question

Explain each line of the following code (Briefly) and give an overall reflection on using these particular functions.

#include<iostream>
#include<string>
using namespace std;
//declare a struct with field mentioned
struct Unit
{
   string unit_code;
   int unit_credict_hrs;
   int unit_semister_study;
   string prerequisites;
   string post_requisites;
   string number_post_requisites;
};
int main()
{
   Unit unit1;
   string str;
   cout << "Enter a tring: ";
   getline(cin, str);
   size_t index = 0;
   string tok,t, del=",";
   string delimit = ";";
   int j = 0,i;
   while ((index = str.find(";")) != std::string::npos)
   {
       tok = str.substr(0, index);
       //std::cout << tok << std::endl;
       str.erase(0, index + delimit.length());
       switch (j)
       {
       case 0:
           unit1.unit_code = tok;
           break;
       case 1:
           unit1.unit_credict_hrs=stoi(tok);
           break;
       case 2:
           unit1.unit_semister_study=stoi(tok);
           break;
       case 3:
           unit1.prerequisites = tok;
          
                  
           if ((i = str.find(del)) != std::string::npos)
           {
              
               t = str.substr(0, i);
               unit1.post_requisites=t;
               str.erase(0, i + del.length());
              
           }
           del = ";";
           if ((i = str.find(del)) != std::string::npos)
           {
                   t = str.substr(0, i);
                   unit1.number_post_requisites = t;
                   str.erase(0, i + del.length());
          
           }
           break;
       }
       ++j;
   }
   //display the structure of unit1
   cout << "Unit Code: " << unit1.unit_code << endl;
   cout << "Unit credit code: " << unit1.unit_credict_hrs << endl;
   cout << "Unit semister code: " << unit1.unit_semister_study << endl;
   cout << "Unit prerequisites: " << unit1.prerequisites << endl;
   cout << "Unit post_requisites: " << unit1.post_requisites << endl;
   cout << "Unit number of post requisites: " << unit1.number_post_requisites << endl;
}

=====================================================
/*Output
Enter a tring: 123MAT;3;2; 147MAT; 159MAT, 146MAT;
Unit Code: 123MAT
Unit credit code: 3
Unit semister code: 2
Unit prerequisites: 147MAT
Unit post_requisites: 159MAT
Unit number of post requisites: 146MAT
*/

Answer 1

#include<iostream> : It includes iostream header file to use in the program.

#include<string> : It includes string header file to use in the program.

using namespace std; : It is used to avoid writing std:: when using cin,cout etc(cout instead of std::cout)

//declare a struct with field mentioned
struct Unit : Name of structure is unit
{ // Starting of structure definition
   string unit_code; : unit_code is a structure variable of type string to store value seperated from the input string

   int unit_credict_hrs; : integer type variable to store credit hours seperated from the input string

   int unit_semister_study; : It stores integer type data to represent semester study seperated from the input string

   string prerequisites; : It stores prerequisties needed of type string

   string post_requisites; : It stores prerequesties needed of type string

   string number_post_requisites; //Used to stores unit number of post requesties

}; //End of structure defintion

int main() //Main program starts from here , it returns an integer value

{ // Execution of program begins from here

   Unit unit1; // unit1 is a variable declared using structure type Unit,it has access to all variables declared under the structure Unit
   string str; // str is string variable to store strings,it holds input data given by user (eg : 123MAT;3;2; 147MAT; 159MAT, 146MAT; )

   cout << "Enter a string: "; //Display the message "Enter a string"

   getline(cin, str); //Get a line of string from user input and stores to variable str for future reference

   size_t index = 0; //size_t represents size of any object in bytes, here index = 0 bytes

   string tok,t, del=","; // Assigns ' , ' to tok,t,del variables of type string

   string delimit = ";"; //A delimiter ' ; ' is used to split the input string

   int j = 0,i; // j is used in the switch case to store each value seperated by delimiter to strucutre variables members such as ' unit_code ' etc..

// i stores the position in index returned by the find() method .

   while ((index = str.find(";")) != std::string::npos) // index=str.find(";") assigns the position of delimiter ' ; ' returned by find method

// std::string::npos , means end of string as an index value

// index = str.find(";")) != std::string::npos , check whether  the position of ' ; ' is not the end of string.
   { //While begins here

       tok = str.substr(0, index); //tok is assigned the portion of string in 'str' starting from index ' 0 ' to the position upto where ' ; ' is found(index stores the position where the ' ; ' is found)

//Initial case tok="123MAT"

       //std::cout << tok << std::endl; //A comment , that will not execute

// endl is used to print a newline

       str.erase(0, index + delimit.length()); //str.erase(pos1,pos2) ,it erases the string from positions pos1 to pos2 stored in ' str ' and restore the remaining to ' str '

//str.erase(0,index+delimit.length()) means

//str.erase(0,5+1) in intial case

//Now ' str ' becomes " 3;2; 147MAT; 159MAT, 146MAT; "
       switch (j)

//A switch case is used to store the seperated data to its corresponding variables
       {
       case 0:
           unit1.unit_code = tok; //unit1.unit_code is used to access the structure member variable

//unit1.unit_code="123MAT"

           break; //To terminate a case

       case 1:

           unit1.unit_credict_hrs=stoi(tok); // stoi(tok) converts a string to number if possible

//unit1.unit_credict_hrs has value 3
           break;
       case 2:
           unit1.unit_semister_study=stoi(tok); //unit1.unit_semister_study has value 2
           break;
       case 3:
           unit1.prerequisites = tok; //unit1.prerequisites has value 147MAT
          
// here str ="159MAT, 146MAT;"
           if ((i = str.find(del)) != std::string::npos) //Check whether position of ' , ' not equal to end of the string,i = position of ' , ' , i.e. i =6
           {
              
               t = str.substr(0, i); // t = str.substr(0,6) ,i.e. t ="159MAT"

               unit1.post_requisites=t; //unit1.post_requisites = "159MAT"

               str.erase(0, i + del.length()); // here str becomes " 146MAT; "
              
           }
           del = ";"; // here del is assigned ' ; ' by replacing ' , ' to seperate the last value "146MAT"

           if ((i = str.find(del)) != std::string::npos) //here i=6 which is not equal to end of string

//A string is terminated by a null character ' \0 '
           {
                   t = str.substr(0, i); // t has the value "146MAT"

                   unit1.number_post_requisites = t; //unit1.number_post_requisites has value "146MAT"

                   str.erase(0, i + del.length()); //erase the part of string from index value 0 to i + del.length() ,i.e. 0 to 7.

//Now finally the string ' str ' is empty,all the values are seperated and stored in corresponding variables.
          
           }
           break;
       }
       ++j; //j value is pre-incremented each time to goto next case of switch,++j = j=j+1
   }
   //display the structure of unit1

//Display the values seperated and stored in corresponding variables.

//endl is used to begin with a newline

   cout << "Unit Code: " << unit1.unit_code << endl;
   cout << "Unit credit code: " << unit1.unit_credict_hrs << endl;
   cout << "Unit semister code: " << unit1.unit_semister_study << endl;
   cout << "Unit prerequisites: " << unit1.prerequisites << endl;
   cout << "Unit post_requisites: " << unit1.post_requisites << endl;
   cout << "Unit number of post requisites: " << unit1.number_post_requisites << endl;
}

This program is used to seperate the value from the string entered by the user and store the seperated value to its corresponding variables defined in the structure that can be accessed by the structure variable ' unit1 '.Here a seperate a value we mainly use a ' ; '.

Thus we get the output as :

Enter a string: 123MAT;3;2; 147MAT; 159MAT, 146MAT;
Unit Code: 123MAT
Unit credit code: 3
Unit semister code: 2
Unit prerequisites: 147MAT
Unit post_requisites: 159MAT
Unit number of post requisites: 146MAT