Disclaimer:
I am a beginner in competitive programming, and this is me documenting my learnings. So, anything I say is just what I think at the moment and should not be taken as hard truths.
char to int
main() {
char c = '5';
int num = c - '0';
cout << num << endl;
// OR
int number = atoi(&c);
cout << number << endl;
}
int to char [only 0-9]
main() {
int num = 5;
char c = num + '0';
cout << c << endl; // output: 5
}
string to int
main() {
string s = "256alphabet";
int num = stoi(s);
cout << num << endl; // output: 256
}
stoi will parse any string and return integer. Additonally takes the base as parameter.
main() {
string s = "001010";
int num = stoi(s, nullptr, 2);
cout << num << endl; // output: 10
}
int to string
main() {
int num = 256;
string s = to_string(num);
cout << s << endl; // output: 256
}
string to vector<char>
#define all(x) begin(x), end(x)
main() {
string s = "5555";
vector<char> v(all(s));
for(auto& c: v) cout << c << ' '; // output: 5 5 5 5
}
vector<char> to string
#define all(x) begin(x), end(x)
main() {
vector<char> v = {'1', '2', '3', '4', '5'};
string s(all(v));
cout << s << endl; // output: 12345
}
vector<int> to string
main() {
vector<int> v = {12345, 54321};
string s;
for(auto& e: v) s.append(to_string(e));
cout << s << endl;
}
string to vector<int>
main() {
string s = "12345";
vector<int> v;
for(auto& c: s) v.push_back(c-'0');
// OR
vector<int> v_new;
transform(all(s), back_inserter(v_new), [](auto& c) { return c-'0'; });
}
Okay! Now we understand basic transformation from one form to another.
Now let us see some base conversions.
base 10 to base 2 [decimal to binary]
main() {
int num = 5; // binary : 0101
string binary = bitset<8>(num).to_string();
cout << binary << endl; // output: 00000101
}
decimal to hex|oct [ int -> string ]
main() {
int num = 16; // hex: 10
stringstream ss;
ss << std::hex << num;
cout << ss.str() << endl; // output: 10
// for oct
ss << std::dec << num;
cout << ss.str() << endl; // output: 20
}
some base to another base(dec/hex/oct) [ string -> string ]
main() {
string num = "16";
stringstream ss;
// consider s to be decimal
// decimal to hex
int initial_base = 10;
ss << std::hex << stoi(num, nullptr, initial_base);
cout << ss.str() << endl; // output: 10
}
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