START TO GIVE EACH LINE COMMENTS

#include <iostream>//This is a header
using namespace std;//this is for not used std before cout
int main(){//this is default
cout << "How to write meaningfull code";//print out in terminal
return 0;//default
}//closed bracket

If you comment each line of code you create a very readfull code for others

START WRITE VERY LESS CODE

#include<iostream>
using namespace std;
int main(){
int a,b;
a = 10;
b = 20;
}

#include<iostream>
using namespace std;
int main(){
int a = 10,b = 20;
}

See on the top side both are doing same thing but in the but side is less is a example of write less code. If you write less but meaningfull code you have a change to make your program less size..