变量a定义为double代表双精度数，而scanf()用%lf表示双精度。用%f代表浮点数。上面语句可以改为： double a; scanf("%lf", &a);

举例如下：

example：

int a;
long int b;
unsigned int c;
float d;
double e;
long double f;
char s[100];

scanf("%d", &a);  // store an int
scanf(" %d", &a); // eat any whitespace, then store an int
scanf("%s", s); // store a string
scanf("%Lf", &f); // store a long double

// store an unsigned, read all whitespace, then store a long int:
scanf("%u %ld", &c, &b);

// store an int, read whitespace, read "blendo", read whitespace,
// and store a float:
scanf("%d blendo %f", &a, &d);

// read all whitespace, then store all characters up to a newline
scanf(" %[^\n]", s);

// store a float, read (and ignore) an int, then store a double:
scanf("%f %*d %lf", &d, &e);

// store 10 characters:
scanf("%10c", s);