x += 1; what is this in C?

An assignment statement evaluates the expression on the right side of the equal sign first and then assigns that value to the variable on the left side of the =. This makes it possible to use the same variable on both sides of an assignment statement, which is frequently done in programming. For example:
 
int x = 3;
x = x + 1; /* x is now 4 */
 
To shorten this type of assignment statement, C offers the += assignment operator. The statement above can be written as
 
x += 1; /* x = x + 1 */