How to Quickly Transition from C to C++

First, the transition mentioned here refers to applications in algorithm competitions, so please do not get it wrong.Welcome to join the QQ group: 784980490. In algorithm competitions, the main differences between C and C++ are as follows:

STL Containers – The Ultimate Tool for Competitions

In C++, many containers are pre-written, which simplifies programming and saves some unimportant work.For example:

// vector - dynamic array
vector<int> v = {1, 2, 3};
v.push_back(4);  // insert at the end
v.pop_back();    // remove from the end
sort(v.begin(), v.end());  // sort

// queue - queue
queue<int> q;
q.push(1);
q.pop();

// stack - stack
stack<int> s;
s.push(1);
s.pop();

// set - ordered set
set<int> st;
st.insert(3);
st.erase(2);
if (st.find(3) != st.end()) {}  // find

// map - key-value pair
map<string, int> mp;
mp["hello"] = 1;
mp.count("hello");  // find key

Algorithm Header Files – The Cheat Tool

The richness of header files greatly simplifies some calculations, such as sorting, where a single sort is enough, and binary search, etc.

vector<int> v = {3, 1, 4, 1, 5};
// sort
sort(v.begin(), v.end());  // default ascending
sort(v.begin(), v.end(), greater<int>());  // descending
// find
auto it = find(v.begin(), v.end(), 4);
if (it != v.end()) {}  // found
// binary search
bool exists = binary_search(v.begin(), v.end(), 3);
// reverse
reverse(v.begin(), v.end());
// max and min values
int max_val = *max_element(v.begin(), v.end());
int min_val = *min_element(v.begin(), v.end());

String Handling

In C++, strings are introduced, which are commonly referred to as character arrays in C.

#include <string>
string str = "hello";
str += " world";  // string concatenation
// common operations
str.length();     // length
str.substr(0, 5); // substring
str.find("world"); // find
stoi(str);        // string to integer
to_string(123);   // number to string

So how should one proceed?First, the most common is to speed up input and output.

// C language
scanf();
printf();
// C++
cin cout

And the STL containers (must master, very convenient):

vector<int> v;      // dynamic array - most commonly used
queue<int> q;       // queue - essential for BFS
stack<int> st;      // stack
string s;           // string - much more convenient than char[]
pair<int,int> p;    // pair

Some algorithm functions:

sort(v.begin(), v.end());                    // sort
reverse(v.begin(), v.end());                 // reverse
max_element(v.begin(), v.end());             // maximum
binary_search(v.begin(), v.end(), target);   // binary search

Finally, there’s the universal header (commonly used in algorithm competitions)

#include <bits/stdc++.h>  

As for other conventions, they are generally consistent.