Shortening Code

Type Names The command typedef can be used to give a short name to a data type. For example, the name long long is long, so we can define a short name ll as follows:

typedef long long ll;
After this, the code
long long a = 123456789;
long long b = 987654321;
cout << a*b << “\n”;

can be shortened as follows:

ll a = 123456789;
ll b = 987654321;
cout << a*b << “\n”;

The command typedef can also be used with more complex types. For example, the following code gives the name vi for a vector of integers, and the name pi for a pair that contains two integers.

typedef vector<int> vi;
typedef pair<int,int> pi;

Macros Another way to shorten code is to define macros. A macro specifies that certain strings in the code will be changed before the compilation. In C++, macros are defined using the #define keyword.
For example, we can define the following macros:

#define F first
#define S second
#define PB push_back
#define MP make_pair

After this, the code

v.push_back(make_pair(y1,x1));
v.push_back(make_pair(y2,x2));
int d = v[i].first+v[i].second;

can be shortened as follows:

v.PB(MP(y1,x1));
v.PB(MP(y2,x2));
int d = v[i].F+v[i].S;

A macro can also have parameters, which makes it possible to shorten loops and other structures. For example, we can define the following macro:

#define REP(i,a,b) for (int i = a; i <= b; i++)
After this, the code
for (int i = 1; i <= n; i++) {
search(i);
}

can be shortened as follows:

REP(i,1,n) {
search(i);
}