### 5.3 Combined Initialization and Assignment Functions

For convenience, GMP provides a parallel series of initialize-and-set functions which initialize the output and then store the value there. These functions’ names have the form `mpz_init_set…`

Here is an example of using one:

    {
      mpz_t pie;
      mpz_init_set_str (pie, "3141592653589793238462643383279502884", 10);
      …
      mpz_sub (pie, …);
      …
      mpz_clear (pie);
    }

Once the integer has been initialized by any of the `mpz_init_set…` functions, it can be used as the source or destination operand for the ordinary integer functions. Don’t use an initialize-and-set function on a variable already initialized!

Function: void mpz_init_set (mpz_t rop, const mpz_t op)
Function: void mpz_init_set_ui (mpz_t rop, unsigned long int op)
Function: void mpz_init_set_si (mpz_t rop, signed long int op)
Function: void mpz_init_set_d (mpz_t rop, double op)

  Initialize rop with limb space and set the initial numeric value from op.

Function: int mpz_init_set_str (mpz_t rop, const char *str, int base)

  Initialize rop and set its value like `mpz_set_str` (see its documentation above for details).

  If the string is a correct base base number, the function returns 0; if an error occurs it returns -1. rop is initialized even if an error occurs. (I.e., you have to call `mpz_clear` for it.)