Expressions in c are basically the building blocks of statements, which them self are used to build your program. The most simple expressions are just values, variables or even functions. You can chain these simple expressions to even bigger expressions with operators. The semicolon at the end turns it into a statement.

C has many different operators. Arithmetic ones like + and -, boolean logic like && and ||, bit-wise logic and shifts like & or <<, assignment = and many more. Here is a list of all the operators.

Try out some operators to build expressions and see how they effect the evaluated output.