C vs C++ – 15 Key Differences

In this lesson: Difference between C and C++ — procedural vs OOP, printf vs cout, malloc vs new, struct vs class — table and code.

C and C++ in one paragraph

C was created by Dennis Ritchie at Bell Labs in 1972 to write the UNIX operating system. It is small, fast and close to the hardware. C++ was created by Bjarne Stroustrup, starting in 1979, as "C with Classes": it keeps nearly all of C and adds object-oriented programming and many safety and productivity features. C++ is standardised by ISO; major versions are C++98, C++11, C++14, C++17, C++20 and C++23.

Difference between C and C++ (table)

Side by side: input and output

/* C */
#include <stdio.h>
int main(void) {
    int age;
    printf("Enter age: ");
    scanf("%d", &age);
    printf("Next year you will be %d\n", age + 1);
    return 0;
}

// C++
#include <iostream>
int main() {
    int age;
    std::cout << "Enter age: ";
    std::cin >> age;
    std::cout << "Next year you will be " << age + 1 << "\n";
    return 0;
}

C++ streams know the type of each variable, so there are no format specifiers like %d to get wrong, and no & needed for input.

Side by side: dynamic memory

/* C */
int *marks = (int *) malloc(5 * sizeof(int));
/* ... */
free(marks);

// C++ (classic)
int* marks = new int[5];
// ...
delete[] marks;

// C++ (modern — no manual free at all)
std::vector<int> marks(5);

new calls constructors and needs no cast or sizeof. Modern C++ goes further: containers and smart pointers free memory automatically.

struct in C vs class in C++

/* C: data only; functions live outside */
struct Student { char name[30]; int marks; };
void print(struct Student s) { printf("%s %d\n", s.name, s.marks); }

// C++: data and behaviour together, with access control
class Student {
    std::string name;
    int marks;
public:
    Student(std::string n, int m) : name(n), marks(m) {}
    void print() const { std::cout << name << " " << marks << "\n"; }
};

In C++, a struct can also have member functions; the only difference from class is that members are public by default.

Overloading and references

// Only possible in C++
int area(int side)            { return side * side; }
int area(int l, int b)        { return l * b; }
void addBonus(int& marks)     { marks += 5; }   // reference: no * or &x needed

int m = 70;
addBonus(m);                  // m becomes 75

In C you would need two function names (area_square, area_rect) and a pointer parameter (void addBonus(int *m) called as addBonus(&m)).

What is the same in both

• Basic data types (int, char, float, double), operators and expressions.
• if, switch, for, while, do-while, break, continue.
• Arrays, pointers and pointer arithmetic.
• Functions, recursion and the preprocessor (#include, #define).
• The C standard library, available in C++ as <cstdio>, <cmath>, <cstring> and so on.

Which one to use?

Common misconceptions

• "C++ is just C with classes" — modern C++ also has templates, the STL, lambdas, smart pointers and much more.
• "C code always compiles in C++" — not if it uses C++ keywords as names or relies on implicit void* conversion.
• "cout is slower, so C++ is slower" — I/O speed depends on settings like std::ios::sync_with_stdio(false); computation speed is the same.
• "struct in C++ cannot have functions" — it can.

Summary

• C is procedural; C++ adds OOP, generic programming and many safety features.
• C++ has classes, references, overloading, namespaces, exceptions, templates and the STL.
• printf/scanf → cout/cin; malloc/free → new/delete or, better, containers and smart pointers.
• Most C code is valid C++, but not all.
• For the same algorithm, both are equally fast.

Related: introduction to C++, OOP concepts, C tutorial: C vs C++.