Difference between -= and =- in C++ and C?

I often confuse both "-=" and "=-", like what is the exact difference between them?

int main()
{
    int x=10, a=-3;
    x=-a;
    printf("%d",x);

    return 0;
}

Output

3

>Solution :

-= is a compound assignment operator. =- is two operators applied seperately.

While

a =- 3;

is the same as

a = (-3);

This

x -= a;

is more or less equivalent to

x = x - a;

"More or less" because operators can be overloaded (in C++) and typically the compound operator avoids the temporary right hand side.

Btw you are using =- twice in your code while the questions asks for += vs =+. += is a compound operator as well.