C++Increment and DecrementIncrement Operator

Understanding the ++ Increment Operator in C++

The increment operator ++ is a unary operator in C++ used to increase a variable’s value by 1.

It comes in two forms:

  • Prefix increment: ++x
  • Postfix increment: x++

Syntax

++x;  // Prefix increment
x++;  // Postfix increment

Prefix vs Postfix

FormDescriptionReturns
++xIncrements first, then returns new valueNew value
x++Returns current value, then incrementsOriginal value

Example with Integers

increment_integers.cpp
#include <iostream>
int main() {
    int a = 5;
    std::cout << "Prefix: " << ++a << std::endl;  // Output: 6
    std::cout << "Postfix: " << a++ << std::endl; // Output: 6
    std::cout << "Now a = " << a << std::endl;    // Output: 7
    return 0;
}

Example in a Loop

increment_loop.cpp
#include <iostream>
int main() {
    for (int i = 0; i < 3; ++i) {
        std::cout << "i = " << i << std::endl;
    }
    return 0;
}

Explanation:

  • ++i is often used in loops for performance (especially with complex types), but functionally similar to i++ for basic types like int.

Example with char Type

increment_char.cpp
#include <iostream>
int main() {
    char ch = 'A';
    ++ch;
    std::cout << "ch = " << ch << std::endl;  // Output: B
    return 0;
}

Explanation:

  • Characters are stored as ASCII codes. 'A' is 65, so ++ch becomes 'B' (66).

Example with Pointers

increment_pointer.cpp
#include <iostream>
int main() {
    int arr[] = {10, 20, 30};
    int* ptr = arr;
    std::cout << *ptr << std::endl;    // 10
    std::cout << *(++ptr) << std::endl; // 20
    return 0;
}

Example with Arrays

increment_array.cpp
#include <iostream>
int main() {
    int arr[3] = {1, 2, 3};
    for (int i = 0; i < 3; i++) {
        arr[i]++;
        std::cout << arr[i] << " ";
    }
    return 0;
}

Output:

2 3 4

Example with User-Defined Class (Operator Overloading)

increment_overload.cpp
#include <iostream>
class Counter {
    int count;
public:
    Counter(int c = 0) : count(c) {}
    Counter& operator++() {   // Prefix
        ++count;
        return *this;
    }
    Counter operator++(int) { // Postfix
        Counter temp = *this;
        count++;
        return temp;
    }
    void show() const { std::cout << "Count = " << count << std::endl; }
};
 
int main() {
    Counter c;
    ++c;
    c.show();  // 1
    c++;
    c.show();  // 2
    return 0;
}

Invalid Use Cases

increment_invalid.cpp
// float x = 1.2;
// ++(x + 1); // ❌ Invalid: x + 1 is an r-value

Summary Table

ContextWorks?ExampleNotes
intYes++x, x++Increments by 1
charYes++chWorks with ASCII codes
float/doubleYes++fAlso increments by 1
pointersYes++ptrMoves pointer to next element
arrayYesarr[i]++Can modify array elements
custom classYesOverload ++Define behavior using operator overloading
r-valueNo++(x+1)❌ Cannot increment temporary values

Use Cases

  • Counting iterations
  • Navigating arrays with pointers
  • Character manipulation
  • User-defined objects that represent counters, indices, etc.

Conclusion

The ++ operator is one of the most commonly used and fundamental operators in C++. Understanding the difference between prefix and postfix and their behavior in various contexts (like loops, pointers, and custom classes) is key to writing clear and efficient C++ code.

Right shift and assignDecrement Operator