C/C++ Basics

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17 December 2024 - 4 mins read time
Tags: Study Guide C/C++ Software

Basics

Printing

#include <stdio.h>  // C
#include <iostream> // C++

int main() {
    printf("Hello, World!\n");  // C
    std::cout << "Hello, World!" << std::endl;  // C++
    return 0;
}

Variables and Datatypes

int x = 5;         // Integer
float y = 3.14;    // Float
char name[] = "Alice"; // String (C-style)
bool is_valid = true; // Boolean (C++)

Control Flow

// If-Else
if (x > 0) {
    printf("Positive\n");
} else if (x == 0) {
    printf("Zero\n");
} else {
    printf("Negative\n");
}

// Loops
for (int i = 0; i < 5; i++) {  // 0 to 4
    printf("%d\n", i);
}

while (x > 0) {
    printf("%d\n", x);
    x--;
}

Functions

int add(int a, int b) {
    return a + b;
}

int main() {
    printf("%d\n", add(3, 4));  // Output: 7
    return 0;
}

Memory Management

/* Dynamic memory allocation */
int *arr = (int *)malloc(5 * sizeof(int));
arr[0] = 10;
free(arr);  // Free memory

/* C++ version */
int *arr = new int[5];
arr[0] = 10;
delete[] arr;  // Free memory

Data Structures

HashTable

C

typedef struct { 
    char *key; 
    int val; 
    struct Node *next; 
} Node;

unsigned int hash(char *key) {
    unsigned int h = 0;
    while (*key) {
        h = h * 31 + *key++; 
    }
    return h % TABLE_SIZE;
}

void insert(char *key, int val) {
    unsigned int idx = hash(key);
    Node *n = malloc(sizeof(Node)); 
    n->key = key; n->val = val; 
    n->next = table[idx];
    table[idx] = n;
}

int search(char *key) {
    for (Node *n = table[hash(key)]; n; n = n->next)
        if (!strcmp(n->key, key)) {
            return n->val;
        )
    return -1;  // Not found
}

C++

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

unordered_map<string, int> table;
table[key] = val;
int get = table[key];

Array

int nums[3] = {1, 2, 3};
int len = sizeof(nums) / sizeof(nums[0]);
printf("%d\n", nums[0]);

Pointer

int x = 10;
int *p = &x;
printf("%d\n", *p);  // Dereference pointer

void (*func_ptr)() = greet;
func_ptr();  // Calls greet()

Struct

struct Person {
    char name[50];
    int age;
};

struct Person p1 = {"Alice", 30};
printf("%s is %d years old.\n", p1.name, p1.age);

Typedef

typedef unsigned int uint;  // Define a new name for `unsigned int`
uint x = 10;

typedef struct {
    char name[50];
    int age;
} Person;

Person p1 = {"Alice", 30};
printf("%s is %d years old.\n", p1.name, p1.age);

Algorithms

Efficient Sort

C

int compare(const void *a, const void *b)
{
    return (*(int *)a - *(int *)b);
}

int *nums;
int len;
qsort(nums, len, sizeof(int), compare)

CPP

#include <algorithm>
#include <vector>

vector<int> nums;
sort(nums.begin(), nums.end())
// or stable_sort

Class

class Car {
public:
    string brand;
    string model;

    Car(string b, string m) {
        brand = b;
        model = m;
    }

    void drive() {
        cout << brand << " " << model << " is driving." << endl;
    }
};

int main() {
    Car myCar("Tesla", "Model S");
    myCar.drive();
    return 0;
}

Files

In C

FILE *file = fopen("file.txt", "w");
if (file) {
    fprintf(file, "Hello, File!\n");
    fclose(file);
}

In C++

#include <fstream>
using namespace std;

ofstream file("file.txt");
if (file.is_open()) {
    file << "Hello, File!\n";
    file.close();
}

Exceptions

try {
    int x = 10 / 0;
} catch (const exception& e) {

}

STL (C++)

Vector

#include <vector>
using namespace std;

vector<int> nums = {1, 2, 3};
nums.push_back(4);
cout << nums[0] << endl;  // Access first element

Map

#include <map>
using namespace std;

map<string, int> ages;
ages["Alice"] = 30;
cout << ages["Alice"] << endl;  // Output: 30

Set

#include <set>
using namespace std;

set<int> s = {3, 1, 4, 1, 2};
s.insert(5);
cout << *s.begin() << endl;  // Smallest element

Queue

#include <queue>
using namespace std;

queue<int> q;
q.push(10); q.push(20); q.push(30);
cout << q.front() << endl;  // Front element
q.pop();                    // Remove front

Stack

#include <stack>
using namespace std;

stack<int> st;
st.push(10); st.push(20);
cout << st.top() << endl;   // Top element
st.pop();                   // Remove top

Lambda and Algorithms

#include <algorithm>
#include <vector>
using namespace std;

vector<int> nums = {1, 2, 3, 4, 5};
auto is_even = [](int x) { return x % 2 == 0; };
nums.erase(remove_if(nums.begin(), nums.end(), is_even), nums.end());

Input and Output

C

int x;
scanf("%d", &x);
printf("%d\n", x);

C++

int x;
cin >> x;
cout << x << endl;

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