What is the difference between a++ and ++a?

Popular languages, like C, C++ and Java, have increment ++ and decrement -- operators that allow you to increment and decrement variable values.

To increment a value, you can do a++ (post-increment) or ++a (pre-increment):

int a = 1;
a++;
printf("%d", a);  // prints 2

int a = 1;
++a;
printf("%d", a);  // prints 2

It seems as though the operator’s position before or after the variable name does not make any difference.

However, the ++ position can make a difference when you are reading the value of the variable in the same statement. More precisely, the post-increment a++ and the pre-increment ++a have different precedence.

For example:

int a = 1;
int b = a++;
printf("%d", b);  // prints 1

int a = 1;
int b = ++a;
printf("%d", b);  // prints 2

As you can see, a++ returns the value of a before incrementing, and ++a returns the value of a after it has been incremented.

Code examples

Let’s understand the a++ operation behavior by observing the output of the following code.

#include <iostream>
int main() {
    int a, b;
    // Post-increment
    a = 1;
    b = a++;
    std::cout << b << " ";  // prints 1
    std::cout << a << " ";  // prints 2
    return 0;
}

The a++ operation

Let's discuss the above C++ code:

Line 7: assigning 1 to variable a.
Line 8: using the post-increment operator a++ . It increments the value of a after the value has been assigned to b. Therefore, b gets the original value of a (which is 1), and then a is incremented by 1.

Let’s understand the ++a operation behavior by observing the output of the following code.

#include <iostream>
int main() {
    int a, b;
    // Post-increment
    a = 1;
    b = ++a;
    std::cout << b << " ";  // prints 1
    std::cout << a << " ";  // prints 2
    return 0;
}

The ++a operation

Let's discuss the above C++ code:

Line 7: assigning 1 to variable a.
Line 8: using the pre-increment operator ++a . The value of the variable a is first incremented and then used in the expression. This means that a is incremented by 1 before its value is assigned to b.

Quiz!

What is the output of the following C++ code snippet?

#include <iostream>

int main() {
    int a = 5;
    int b = 10;

    std::cout << a++-++b;

    return 0;
}

-6

Question 1 of 20 attempted

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