sqlParser.cpp

#include<iostream>
#include<algorithm> //for find method used to check for a value in a vector.
#include<fstream>
#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#include<vector>
#include<limits>

using namespace std;

struct tableList { //this is synonym to database used in sql which contains multiple tables.
 vector<struct table*> database;
};
struct tableList* db1 = new(tableList); //creating only one database and all tables will be populated in same.

struct table { //datastructure for tables.
 string tableName;
 vector<string> headings;
 vector<string> headingType; //using without the data type for attributes
 vector<vector<string> > tuple;
};


int fileInput(string fileName) { //the fileName should be present at same
 ifstream in (fileName); // location where this program is executed.
 if(!in) {
 cout<<"cannot open file\n"<<endl;
 return 1;
 }
 else {
 struct table* temp = new(table);

 db1->database.push_back(temp);
 cout<<"size of db1"<<db1->database.size()<<endl;

 getline(in, temp->tableName);
 cout<<"name for this entered table is "<<temp->tableName<<endl;
 vector<string> head;
 string heads, token;
 getline(in, heads);

 for(unsigned int i = 0; i < heads.size(); ++i) {
 if(heads[i] != ' ')
 token += heads[i];
 else {
 head.push_back(token);
 token.erase(token.begin(), token.end());
 }
 }
 head.push_back(token); //to get last value which doesnot hava a tailing space

 for(unsigned int i = 0; i < head.size(); i += 2) {
 temp->headings.push_back(head[i]);
 // cout<<head[i]<<" "<<head[i+1]<<endl;
 temp->headingType.push_back(head[i+1]);
 }

 for(auto i = temp->headings.begin(); i != temp->headings.end(); ++i)
 cout<<*i<<"\t\t";
 cout<<endl;

 vector<string> row;
 while(!in.eof()) {
 token.erase(token.begin(), token.end());
 getline(in, heads);
 for (unsigned int i = 0; i < heads.size(); ++i) {
 if(heads[i] != ',')
 token += heads[i];
 else {
 row.push_back(token);
 token.erase(token.begin(), token.end());
 }
 }
 row.push_back(token);

 temp->tuple.push_back(row);
 row.clear();
 }
 for(unsigned int i = 0 ; i < temp->tuple.size(); ++i) {
 for(unsigned int j = 0; j < temp->tuple[i].size(); ++j)
 cout<<temp->tuple[i][j]<<"\t";
 cout<<endl;
 }
 }
 return 0;
}


int checkPresenceOfTable(string tableName) { // this check if tableName is present in collection.
 struct table* temp;
 for(unsigned int I = 0; I != db1->database.size(); ++I) {
 temp = db1->database[I];
 if(temp->tableName == tableName)
 return 1;
 }
 return 0;
}

struct table* assignTable(string tableName) { //this returns pointer to an existing table from the collection.
 struct table* temp;
 for(unsigned int I = 0; I != db1->database.size(); ++I) {
 temp = db1->database[I];
 if(temp->tableName == tableName)
 return temp;
 }
 return nullptr;
}


int renameTable(string tableName, string newTableName) {
 struct table* temp;
 for(unsigned int I = 0; I != db1->database.size(); ++I) {
 temp = db1->database[I];
 if(temp->tableName == tableName) {
 temp->tableName = newTableName;
 return 1;
 }
 }
 return 0;
}


string Union(string table1, string table2) {
 if(table1 == table2) {
 cout<<"Names of both tables are same"<<endl;
 return string();
 }

 if ( checkPresenceOfTable(table1) and checkPresenceOfTable(table2) ) {
 struct table* tab1 = assignTable(table1);
 struct table* tab2 = assignTable(table2);

 if(tab1 == nullptr or tab2 == nullptr) {
 cout<<"memory could not be allocated"<<endl;
 return string();
 }

 struct table* temp = new(table);
 temp->tableName = table1+table2;
 cout<<"new name for newly created table is "<<temp->tableName<<endl;
 
// cout<<"size of db1"<<db1->database.size()<<endl;
 db1->database.push_back(temp);
// cout<<"size of db1"<<db1->database.size()<<endl;

// making heading vector for new table by headings of parent table.
// and printing headings for display.
 for(auto i = tab1->headings.begin(); i != tab1->headings.end(); ++i) {
 cout<<*i<<"\t\t";
 temp->headings.push_back(*i);
 }
 cout<<endl;

// making heading type for new table by heading of parent table.
 for(auto i = tab1->headingType.begin(); i != tab1->headingType.end(); ++i)
 temp->headingType.push_back(*i);

 vector<string> row;
 for(unsigned int i = 0 ; i < tab1->tuple.size(); ++i) {
 for(unsigned int j = 0; j < tab1->tuple[i].size(); ++j)
// cout<<temp->tuple[i][j]<<"\t";
 row.push_back(tab1->tuple[i][j]);
 temp->tuple.push_back(row);
 for(auto it = row.begin(); it != row.end(); ++it)
 cout<<*it<<"\t\t";
 cout<<endl;
 row.clear();
 }
 
 for(unsigned int i = 0 ; i < tab2->tuple.size(); ++i) {
 for(unsigned int j = 0; j < tab2->tuple[i].size(); ++j)
// cout<<temp->tuple[i][j]<<"\t";
 row.push_back(tab2->tuple[i][j]);
 if (find(temp->tuple.begin(), temp->tuple.end(), row) == temp->tuple.end()) {
 temp->tuple.push_back(row);
 for(auto it = row.begin(); it != row.end(); ++it)
 cout<<*it<<"\t\t";
 cout<<endl;
 }
 row.clear();
 }
 return temp->tableName;
 }
 return string();
}


string intersection(string table1, string table2) {
 if(table1 == table2) {
 cout<<"Names of both tables are same"<<endl;
 return string();
 }

 if ( checkPresenceOfTable(table1) and checkPresenceOfTable(table2) ) {
 struct table* tab1 = assignTable(table1);
 struct table* tab2 = assignTable(table2);

 if(tab1 == nullptr or tab2 == nullptr) {
 cout<<"memory could not be allocated"<<endl;
 return string();
 }

 struct table* temp = new(table);
 temp->tableName = table1+table2;
 cout<<"new name for newly created table is "<<temp->tableName<<endl;
 
 db1->database.push_back(temp);

// making heading vector for new table by headings of parent table.
// and printing headings for display.
 for(auto i = tab1->headings.begin(); i != tab1->headings.end(); ++i) {
 cout<<*i<<"\t\t";
 temp->headings.push_back(*i);
 }
 cout<<endl;

// making heading type for new table by heading of parent table.
 for(auto i = tab1->headingType.begin(); i != tab1->headingType.end(); ++i)
 temp->headingType.push_back(*i);

 vector<string> row;
 for(unsigned int i = 0 ; i < tab2->tuple.size(); ++i) {
 for(unsigned int j = 0; j < tab2->tuple[i].size(); ++j)
 row.push_back(tab2->tuple[i][j]);
 if (find(tab1->tuple.begin(), tab1->tuple.end(), row) != tab1->tuple.end()) {
 temp->tuple.push_back(row);
 for(auto it = row.begin(); it != row.end(); ++it)
 cout<<*it<<"\t\t";
 cout<<endl;
 }
 row.clear();
 }
 return temp->tableName;
 }
 return string();
}



string setDifference(string table1, string table2, string table3) {
 if(table1 == table2) {
 cout<<"Names of both tables are same"<<endl;
 return string();
 }

 if ( checkPresenceOfTable(table1) and checkPresenceOfTable(table2) ) {
 struct table* tab1 = assignTable(table1);
 struct table* tab2 = assignTable(table2);

 if(tab1 == nullptr or tab2 == nullptr) {
 cout<<"memory could not be allocated"<<endl;
 return string();
 }

 struct table* temp = new(table);
 temp->tableName = table3;
 cout<<"new name for newly created table is "<<temp->tableName<<endl;
 
 db1->database.push_back(temp);

// making heading vector for new table by headings of parent table.
 for(auto i = tab1->headings.begin(); i != tab1->headings.end(); ++i) {
 cout<<*i<<"\t\t";
 temp->headings.push_back(*i);
 }
 cout<<endl;
// making heading type for new table by heading of parent table.
 for(auto i = tab1->headingType.begin(); i != tab1->headingType.end(); ++i)
 temp->headingType.push_back(*i);

 vector<string> row;
 for(unsigned int i = 0 ; i < tab1->tuple.size(); ++i) {
 for(unsigned int j = 0; j < tab1->tuple[i].size(); ++j)
// cout<<temp->tuple[i][j]<<"\t";
 row.push_back(tab1->tuple[i][j]);
 temp->tuple.push_back(row);
 for(auto it = row.begin(); it != row.end(); ++it)
 cout<<*it<<"\t\t";
 cout<<endl;
 row.clear();
 }
 
 for(unsigned int i = 0 ; i < tab2->tuple.size(); ++i) {
 for(unsigned int j = 0; j < tab2->tuple[i].size(); ++j)
// cout<<temp->tuple[i][j]<<"\t";
 row.push_back(tab2->tuple[i][j]);
 auto iter = find(temp->tuple.begin(), temp->tuple.end(), row);
 if(iter != temp->tuple.end())
 temp->tuple.erase(iter);
 cout<<"deleted";
 for(auto it = row.begin(); it != row.end(); ++it)
 cout<<*it<<"\t\t";
 cout<<endl;
 row.clear();
 }
 cout<<"Remaining lines in newTable"<<temp->tuple.size()<<endl;

 return temp->tableName;
 }
 return string();
}



string cartesianProduct(vector<string> query) {
 string table1 = query[1];
 string table2 = query[2];

 if(table1 == table2) {
 cout<<"Names of both tables are same"<<endl;
 cout<<"either change the name using renameTable command or check query"<<endl;
 return string();
 }

 if ( checkPresenceOfTable(table1) and checkPresenceOfTable(table2) ) {
 struct table* tab1 = assignTable(table1);
 struct table* tab2 = assignTable(table2);

 if(tab1 == nullptr or tab2 == nullptr) {
 cout<<"memory could not be allocated"<<endl;
 return string();
 }

 struct table* temp = new(table);
 temp->tableName = table1+table2;
 cout<<"new name for newly created table is "<<temp->tableName<<endl;
 
 db1->database.push_back(temp);

// making heading vector for new table by combining two headings of parent tables.
 for(auto i = tab1->headings.begin(); i != tab1->headings.end(); ++i) {
 cout<<*i<<"\t\t";
 temp->headings.push_back(*i);
 }
 for(auto i = tab2->headings.begin(); i != tab2->headings.end(); ++i) {
 cout<<*i<<"\t\t";
 temp->headings.push_back(*i);
 }
 cout<<endl;

// making heading type for new table by combining two headings of parent tables.
 for(auto i = tab1->headingType.begin(); i != tab1->headingType.end(); ++i)
 temp->headingType.push_back(*i);
 for(auto i = tab2->headingType.begin(); i != tab2->headingType.end(); ++i) 
 temp->headingType.push_back(*i);

 for(unsigned int i = 0 ; i < tab1->tuple.size() - 1; ++i) //-1 is substracted because an extra empty line is present in all tables of collection of tables.
 for(unsigned int ii = 0 ; ii < tab2->tuple.size() - 1; ++ii) {
 vector<string> row;
 for(unsigned int j = 0; j < tab1->tuple[i].size(); ++j) 
 row.push_back(tab1->tuple[i][j]);
 for(unsigned int jj = 0; jj < tab2->tuple[ii].size(); ++jj)
 row.push_back(tab2->tuple[ii][jj]);
 temp->tuple.push_back(row);
 }
 
 for(unsigned int ii = 0 ; ii < temp->tuple.size(); ++ii) {
 for(unsigned int ij = 0 ; ij < temp->tuple[ii].size(); ++ij)
 cout<<temp->tuple[ii][ij]<<"\t";
 cout<<endl;
 }
 return temp->tableName;
 }
 else {
 cout<<"Requested table/tables donot exist"<<endl;
 return string();
 }
}



string select(vector<string> query) {
 string RequiredTableName;
 vector <string> attributes;

 auto i = query.begin(); ++i; //to move from select to 1st attribute
 for(; i != query.end(); ++i) {
 if(*i != "from") {
 if(*i != "") {
 attributes.push_back(*i);
 }
 }
 else
 break;
 }

 i++; // to move forward from "from" clause in query vector
 RequiredTableName = *i;
// cout<<"Using data from tableName "<<*i<<endl;

 bool flag = 0; //getting the required table from list of all tables present in the tables collection.
 struct table* temp;
 for(unsigned int I = 0; I != db1->database.size(); ++I) {
 temp = db1->database[I];
 if(temp->tableName == RequiredTableName) {
 flag = 1;
 break;
 }
 }

 if(flag == 0) {
 cout<<"Requested table doesnot exist"<<endl;
 return string();
 }
 else {
// cout<<"yay table exist"<<endl;
 vector <string> clause;
 vector <vector<string> > conditions;

 for(unsigned int i = 0; i < attributes.size(); ++i) {
 if(attributes[i] != "and") {
 clause.push_back(attributes[i]);
 cout<<attributes[i]<<" ";
 }
 else {
 conditions.push_back(clause);
 cout<<endl;
 clause.clear();
 }
 }
 conditions.push_back(clause); //this is needed to get the last clause which will not pass through else block becuase it doesnot have a "and" after it.
 cout<<endl;

// checking if first entry of each clause is present as valid attribute in the table
 flag = 0;
 for(unsigned int i = 0; i < conditions.size(); ++i)
 for(unsigned int j = 0; j < temp->headings.size(); ++j) {
 if(conditions[i][0] == temp->headings[j]) {
// cout<<"checked "<<conditions[i][0]<<endl;
 break;
 }
 else if(j == temp->headings.size() && conditions[i][0] != temp->headings[j]) {
 flag = 1;
 //cout<<"problemo at"<<conditions[i][0]<<endl;
 }
 }

 if (flag == 1) {
 cout<<"requested attribute doesnot exist"<<endl;
 return string();
 }

// cout<<*i<<"check"<<endl;
 struct table* selectedTable = new(table);

 selectedTable->tableName = temp->tableName;
 selectedTable->tableName += "sel";
 cout<<"name of newly created table is "<<selectedTable->tableName<<endl;
 selectedTable->headings = temp->headings;
 selectedTable->headingType = temp->headingType;
 
 db1->database.push_back(selectedTable); // adding new table to collection of tables.

 int flags[temp->tuple.size()];
 fill_n(flags, temp->tuple.size(), -1);

 for(unsigned int i = 0; i < temp->tuple.size(); ++i)
 for(unsigned int k = 0; k < conditions.size(); ++k) {
 for(unsigned int j = 0; j < temp->tuple[i].size(); ++j) {
 if(temp->headings[j] == conditions[k][0]) {
// cout<<conditions[k][0]<<conditions[k][1]<<endl;
 if(conditions[k][1] == "=") {
//cout<<"it came here for checking with ="<<conditions[k][0]<<"and"<<temp->headings[i]<<endl;
 if(temp->tuple[i][j] == conditions[k][2]) {
 if(flags[i] == -1 or flags[i] == 1) //when it's uninitialized or when it's already valid keep it valid for now.
 flags[i] = 1;
 }
 else //when this condition has been already violated.
 flags[i] = 0;
 }
 else if(conditions[k][1] == "!=") {
 if(temp->tuple[i][j] != conditions[k][2]) {
 if(flags[i] == -1 or flags[i] == 1)
 flags[i] = 1;
 else // when the given condition was calculated as false, make it false so it's never needed in future to take of. Though with use of "or" this will fail drastically.
 flags[i] = 0;
 }
 }
//below conditions are fruitful for int and decimal data types only.
 else if(conditions[k][1] == ">" and (temp->headingType[j] == "1" or temp->headingType[j] == "2")) {
 if(stod(temp->tuple[i][j]) > stod(conditions[k][2])) { //converting to double precision number for proper comparison.
 if(flags[i] == -1 or flags[i] == 1)
 flags[i] = 1;
 else
 flags[i] = 0;
 }
 else
 flags[i] = 0;
 }
 else if(conditions[k][1] == "<" and (temp->headingType[j] == "1" or temp->headingType[j] == "2")) {
 if(std::stod(temp->tuple[i][j]) < stod(conditions[k][2])) {
 if(flags[i] == -1 or flags[i] == 1)
 flags[i] = 1;
 else
 flags[i] = 0;
 }
 else
 flags[i] = 0;
 }
 else {
 cout<<"conditional not supported"<<endl;
 cout<<temp->headingType[j]<<conditions[k][2]<<endl;
 return string();
 }
 }
 }
 }
 cout<<"after"<<endl;
 for(auto i = 0; i < temp->tuple.size(); ++i) {
 cout<<flags[i]<<" ";
 if(flags[i] ==1) //inserting all tuples having value of flag as 1
 selectedTable->tuple.push_back(temp->tuple[i]);
 }
 cout<<endl;
 cout<<selectedTable->tuple.size()<<endl;

 return selectedTable->tableName;
 }
}





void rename(vector<string> query) { //format: rename prevAttr newAttr in tableName
 string RequiredTableName;
 auto i = query.begin(); ++i; //to move from rename to prevAttr
 string prevAttrName = *i;
 
 ++i;
 string newAttrName = *i;

 i++; i++; // to move forward from "in" clause in query vector
 RequiredTableName = *i;

 bool flag = 0; //getting the required table from list of all tables present in the tables collection.
 struct table* temp;
 for(unsigned int I = 0; I != db1->database.size(); ++I) {
 temp = db1->database[I];
 if(temp->tableName == RequiredTableName) {
 flag = 1;
 break;
 }
 }

 if(flag == 0) {
 cout<<"Requested table doesnot exist"<<endl;
 return;
 }
 else {
 auto i = temp->headings.begin();
 bool flag = 0;
 for(; i != temp->headings.end(); ++i)
 if(*i == prevAttrName) {
 *i = newAttrName;
 flag = 1;
 cout<<prevAttrName<<" changed to "<<newAttrName<<endl;
 break;
 }
 if(flag == 0)
 cout<<"requested attribute "<<prevAttrName<<" to be changed doesnot exit in "<<RequiredTableName<<endl;
 }
}




string project(vector< string > query) {
 string RequiredTableName;
 vector <string> attributes;

 auto i = query.begin(); ++i; //to move from select to 1st attribute
 for(; i != query.end(); ++i) {
 if(*i != "from") {
 if(*i != "") {
 attributes.push_back(*i);
 }
 }
 else
 break;
 }
 cout<<endl;

 i++; // to move forward from "from" clause in query vector
 RequiredTableName = *i;
// Checking if table of this name exits in collection 
 bool flag = 0; //getting the required table from list of all tables present in the tables collection.
 struct table* temp;
 for(unsigned int I = 0; I != db1->database.size(); ++I) {
 temp = db1->database[I];
 if(temp->tableName == RequiredTableName) {
 flag = 1;
 break;
 }
 }

 if(flag == 0) {
 cout<<"Requested table doesnot exist"<<endl;
 return string();
 }
 else {
// cout<<"table exist"<<endl;
 if(attributes.size() > temp->headings.size()) { //if no. of attributes entered is more than that present in the table
 cout<<"excess attributes asked"<<endl;
 return string();
 }

 struct table* projected = new(table); //constructing new table for record.
 projected->tableName = RequiredTableName;
 projected->tableName += "proj";
 cout<<"name of new table is "<<projected->tableName<<endl;

 // cout<<"size of db1"<<db1->database.size()<<endl;
 db1->database.push_back(projected);
 // cout<<"size of db1"<<db1->database.size()<<endl;

//comparing entered attributers with attributes present in required table
 for(unsigned int i = 0; i < attributes.size(); ++i)
 if(attributes[i] != "") {
 cout<<attributes[i]<<" \t\t";
 projected->headings.push_back(attributes[i]);
 }
 cout<<endl;

 vector<unsigned> indexes;
 flag = 0;
 for(unsigned int i = 0; i < attributes.size(); ++i)
 for(unsigned int j = 0; j < temp->headings.size(); ++j) {
 if(attributes[i] == temp->headings[j]) {
 projected->headingType.push_back(temp->headingType[j]); //entering the corresponding value type for attributes.
 indexes.push_back(j);
 break;
 }
 else if(j == temp->headings.size() && attributes[i] != temp->headings[j]) {
 flag = 1;
// cout<<"problemo at"<<attributes[i]<<endl;
 }
 }

 if(attributes.size() == 1 and attributes[0] == "*") //special case for "*"
 flag = 0;

 if (flag == 1) {
 cout<<"requested attribute doesnot exist"<<endl;
 return string();
 }

 vector<string> row;
 for(unsigned int i = 0 ; i < temp->tuple.size(); ++i) {
 for(unsigned int j = 0; j < temp->tuple[i].size(); ++j)
 if(find(indexes.begin(), indexes.end(), j) != indexes.end()) { //find is used to find a particular value in a vector.defined in algorithm header.
// cout<<temp->tuple[i][j]<<"\t";
 row.push_back(temp->tuple[i][j]);
 }
 if (find(projected->tuple.begin(), projected->tuple.end(), row) == projected->tuple.end()) {
 projected->tuple.push_back(row);
 for(auto it = row.begin(); it != row.end(); ++it)
 cout<<*it<<"\t\t";
 cout<<endl;
 }
 row.clear();
 }
 return projected->tableName;
 }
}




string readLine() {
 string line;
 getline(cin, line);
 return line;
}


vector<string> splitLine(string line) {
 vector<string> tokens;
 string token;
 line += " f"; // to overcome error of not getting last chunk of chars

 int t = (line.end() - line.begin())/sizeof(line[0]);
 for(int i = 0; i < t; ++i) {
 if(line[i]!=' ' and line[i]!='(' and line[i]!=')' and line[i]!=',' and line[i]!=';') { //this is causing proble when " ," or combination of other such characters is used together, segmentation fault occurs.
 token += line[i];
 }
 else {
 tokens.push_back(token);
 token.erase(token.begin(), token.end());
 }
}
 return tokens;
}

void invalid() {
 cout<<"Invalid syntax"<<endl;
}


int execute(std::vector<string> tokens) {
 if (tokens[0] == "exit") {
 cout<<"bye"<<endl;
 return 0;
 }
 else if (tokens[0] == "fileIn" or tokens[0] == "fin") {
 if(tokens.size() == 2)
 fileInput(tokens[1]); //assumed file is in same location as this code.
 else
 invalid();
 }
 else if( tokens[0] == "select" or tokens[0] == "sel") {
 if(tokens.size() > 5)
 select(tokens);
 else
 invalid();
 }
 else if (tokens[0] == "rename" or tokens[0] == "re") {
 rename(tokens);
 }
 else if (tokens[0] == "project" or tokens[0] == "proj") {
 project(tokens);
 }
 else if (tokens[0] == "cartesian product" or tokens[0] == "cp") {
 if(tokens.size() == 3)
 cartesianProduct(tokens);
 else 
 invalid();
 }
 else if (tokens[0] == "check" or tokens[0] == "ch") {
 if(tokens.size() == 2 and tokens[1] != "") {
 if(checkPresenceOfTable(tokens[1]))
 cout<<"table exist with name"<<tokens[1]<<endl;
 else
 cout<<"table with name "<<tokens[1]<<" doesnot exist"<<endl;
 }
 else 
 invalid();
 }
 else if (tokens[0] == "renameTable" or tokens[0] == "reTab") {
 if(tokens.size() == 3) {
 if(renameTable(tokens[1], tokens[2]))
 cout<<"rename successful"<<"now its "<<tokens[2]<<endl;
 else
 cout<<"problem when attempting to change of the table"<<endl;
 }
 else
 invalid();
 }
 else if (tokens[0] == "intersection" or tokens[0] == "inter") {
 if(tokens.size() == 3 and tokens[1] != "" and tokens[2] != "")
 intersection(tokens[1], tokens[2]);
 else
 invalid();
 }
 else if (tokens[0] == "union" or tokens[0] == "uni") {
 if(tokens.size() == 3 and tokens[1] != "" and tokens[2] != "")
 Union(tokens[1], tokens[2]);
 else
 invalid();
 }
 else if (tokens[0] == "setDifference" or tokens[0] == "setdiff") {
 if(tokens.size() == 3 and tokens[1] != "" and tokens[2] != "")
 setDifference(tokens[1], tokens[2], tokens[3]);
 else
 invalid();
 }
 else
 return 1;
}

void loop() {
 string line;
 vector<string> args;
 int status = 1;
 do {
 cout<<"> ";
 line = readLine(); //each line is read
 args = splitLine(line); //split into tokens using(" ",",",";") as seperators.
 status = execute(args);
 } while(status);
}

int main(int argc, char *argv[]) {
 printf("This parser now have following working commands\n");
 printf(" > fileIn\n");
 printf(" > exit\n");
 printf(" > rename\n");
 printf(" > select\n");
 printf(" > project\n");
 printf(" > cartesian product\n");
 printf(" > renameTable \n");
 printf(" > union \n");
 printf(" > setDifference \n");
 printf(" > intersection \n");
 loop(); //main function to act like command prompt
}