Double 函数以整数形式返回

Question

I would like to know why does my double function returns as an integer instead of a decimal. I gave a value of 0.01 to my ic4 to go into the function and expect a return of 0.384615 but instead i get a return of 1.

#include <iostream>
#include <string>
#include <cmath>
#include <math.h>

using namespace std;

double vt = 0.026;
double ic4;

double gm7(double IC7);

int main ()
{
    while(true)
    {
        printf("ao (in dB): ");
        cin >> ao;

        if (ao >= 80)
        {
            printf("IC7 (in Amps): ");
            cin >> ic7;
            cout << "IC7: " << ic7 << endl;
            gm7(ic7);
            cout <<"gm7: " << gm7 << endl;
        }
    
        else
        {
            printf("Choose another ao!\n");
        }
    }
}

double gm7 (double IC7)
{
    return IC7 / vt;
}

Answer 1

gm7 is a function. You are inserting a function into the character stream.

Character streams do no have an insertion operator overloads for functions. However, they do have an overload for bool and function pointers implicitly convert to bool and function implicitly converts to a function pointer. Since the function pointer is not null, it converts to true . true is printed as 1.

PS The example program is ill-formed because it uses undeclared names.

Answer 2

just to clarify the comments

you should do this

int main ()
{
    while(true)
    {
        printf("ao (in dB): ");
        cin >> ao;

        if (ao >= 80)
        {
            printf("IC7 (in Amps): ");
            cin >> ic7;
            cout << "IC7: " << ic7 << endl;
            double gm7res = gm7(ic7); <======
            cout <<"gm7: " << gm7res << endl; <<======
        }
    
        else
        {
            printf("Choose another ao!\n");
        }
    }
}

note you also need to declare a0