#include<bits/stdc++.h>
#include<iomanip> //per stampe ordinate
using namespace std; 

/*============================================
COMPARE FUNCTION COMAPRE 2ND COLUMN ELEMENTS
=============================================*/
#define colonne 9

#define righe 250
int ColonnaDaOrdinare=1;

bool compare_col(const vector<int>& v1,const vector<int>& v2) 
{ 
    return v1[ColonnaDaOrdinare] < v2[ColonnaDaOrdinare]; 
} 

/*==========================================================
FUNCTION TO SORT 2D VECTOR ON THE BASIS OF PARTICULAR COLUMN
===========================================================*/
void sorting(vector<vector<int>>A)
{
    //n contain no.of rows
    int n=A.size();
    //m contain no. of columns
    int m=A[1].size();
    cout<<"Sorting 2D vector on the basis of 2nd column\n\n";
    // Displaying the 2D vector after sorting 
    cout << "2D vector before sorting :"<<endl<<endl; 
    for (int i=0; i<n; i++) 
    { 
        for (int j=0; j<m ;j++)
        {
            cout <<setw(5)<< A[i][j] << " "; 
        }cout<<endl;
    } 
cout<<endl;
    // Using sort() function to sort.
    //compare_col parameter used to compare col elements.
    //And sort accordingly.
    sort(A.begin(), A.end(),compare_col); 

    // Displaying the 2D vector after sorting 
    cout << "2D vector after sorting : Colonna "<<ColonnaDaOrdinare<<endl<<endl;
	for (int j=0; j<m ;j++) {
	cout << setw(5)<<j<<" ";}
	
	 cout<< endl;
    for (int i=0; i<n; i++) 
    { 
        for (int j=0; j<m ;j++) 
            {
            	
                cout <<setw(5)<< A[i][j] << " "; //setw stampa ordinata
            }cout << endl; 
    } 

}

/*======================================
   MAIN FUNCTION
=======================================*/
int main() 
{ 
 srand(time(0));
    // Initializing 2D vector
     //inserire numero di righe
    //inserire numero di colonne
    
    vector< vector<int> > vect;
	vect.resize(righe);
	
	for (int i = 0; i < righe; i++)
{
    vect[i].resize(colonne);  // resize each of the contained vectors
    vect[i][0] = i+1;
    for (int c = 1; c <= colonne ; c++){
	
    vect[i][c] = rand()%31000+1;}
    
}
    //Calling sorting function
    sorting(vect); 

    return 0; 
}

C++ Online Compiler

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Read inputs from stdin

OneCompiler's C++ online compiler supports stdin and users can give inputs to programs using the STDIN textbox under the I/O tab. Following is a sample program which takes name as input and print your name with hello.

#include <iostream>
#include <string>
using namespace std;

int main() 
{
    string name;
    cout << "Enter name:";
    getline (cin, name);
    cout << "Hello " << name;
    return 0;
}

About C++

C++ is a widely used middle-level programming language.

  • Supports different platforms like Windows, various Linux flavours, MacOS etc
  • C++ supports OOPS concepts like Inheritance, Polymorphism, Encapsulation and Abstraction.
  • Case-sensitive
  • C++ is a compiler based language
  • C++ supports structured programming language
  • C++ provides alot of inbuilt functions and also supports dynamic memory allocation.
  • Like C, C++ also allows you to play with memory using Pointers.

Syntax help

Loops

1. If-Else:

When ever you want to perform a set of operations based on a condition If-Else is used.

if(conditional-expression) {
   //code
}
else {
   //code
}

You can also use if-else for nested Ifs and If-Else-If ladder when multiple conditions are to be performed on a single variable.

2. Switch:

Switch is an alternative to If-Else-If ladder.

switch(conditional-expression){    
case value1:    
 // code    
 break;  // optional  
case value2:    
 // code    
 break;  // optional  
......    
    
default:     
 code to be executed when all the above cases are not matched;    
}

3. For:

For loop is used to iterate a set of statements based on a condition.

for(Initialization; Condition; Increment/decrement){  
  //code  
}

4. While:

While is also used to iterate a set of statements based on a condition. Usually while is preferred when number of iterations are not known in advance.

while (condition) {  
// code 
}

5. Do-While:

Do-while is also used to iterate a set of statements based on a condition. It is mostly used when you need to execute the statements atleast once.

do {  
 // code 
} while (condition);

Functions

Function is a sub-routine which contains set of statements. Usually functions are written when multiple calls are required to same set of statements which increases re-usuability and modularity. Function gets run only when it is called.

How to declare a Function:

return_type function_name(parameters);

How to call a Function:

function_name (parameters)

How to define a Function:

return_type function_name(parameters) {  
 // code
}