动态内存分配输出

Question

int main () {
    double* pvalue  = NULL; // Pointer initialized with null

    pvalue  = new double;   // Request memory for the variable

    *pvalue = 29494.99;     // Store value at allocated address

    cout << "Value of pvalue : " << *pvalue << endl;

    delete pvalue;         // free up the memory.

    return 0;
}

Output:

29495

Why is the output 29495 ?

When I change the value to 29494.4344 , why is the output 29494.4 ?

Answer 1

29494.99 is rounded to 29495.0 for cout << purposes because the default number of significant digits with which cout prints numbers is 6 and zeros at the end are not printed by default.

You can use std::setprecision to change the output precision (requires #include <iomanip> ):

cout << setprecision(7) << "Value of pvalue : " << *pvalue << endl;

prints 29494.99 .

---

29494.4344 is rounded to 29494.4 by default and since the last digit of that is not a zero, it will be printed.