The default storage class for all variables declared inside a function or a block is auto. Auto variables can be only accessed within the block/function they have been declared and not outside them. To access them outside their scope, use a pointer to the very exact memory location where the variables resides. They are assigned a garbage value by default whenever they are declared. As auto is the default, the keyword auto is rarely used. Typically, auto variables are created on the stack.
Code example
int foo (char n, float m) { // n, m are auto variables
int j, k; // j, k are auto variables
}