简单的C++错误:"...未声明(首先使用此功能)"

Question

嘿伙计们,我正在研究我的第一个C++课程.出于某种原因,我在尝试编译时遇到以下错误:

`truncate' undeclared (first use this function)

完整来源:

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

using namespace std;

#define CENTIMETERS_IN_INCH 2.54
#define POUNDS_IN_KILOGRAM 2.2

int main() {
    double feet, inches, centimeters, weight_in_kg, weight_in_lbs;

    // get height in feet and inches
    cout << "Enter height (feet): ";
    cin >> feet;
    cout << "Enter (inches): ";
    cin >> inches;

    // convert feet and inches into centimeters
    centimeters = ((12 * feet) + inches) * CENTIMETERS_IN_INCH;

    // round 2 decimal places and truncate
    centimeters = truncate(centimeters);

    printf("Someone that is %g' %g\" would be %g cm tall", feet, inches, centimeters);

    // weights for bmi of 18.5
    weight_in_kg = truncate(18.5 * centimeters);
    weight_in_lbs = round(weight_in_kg * POUNDS_IN_KILOGRAM);

    printf("18.5 BMI would correspond to about %g kg or %g lbs", weight_in_kg,   weight_in_lbs);

    // weights for bmi of 25
    weight_in_kg = truncate(25 * centimeters);
    weight_in_lbs = round(weight_in_kg * POUNDS_IN_KILOGRAM);

    printf("25.0 BMI would correspond to about %g kg or %g lbs", weight_in_kg, weight_in_lbs);

    // pause output
    cin >> feet;

    return 0;
}

// round result
double round(double d) {
   return floor(d + 0.5);
}

// round and truncate to 1 decimal place
double truncate(double d) {
   return round(double * 10) / 10;
}

任何帮助,将不胜感激.谢谢.

Answer 1

你需要在你的前面申报main:

double truncate(double d);
double round(double d);

您可以在main之前定义您的函数,这也将解决问题:

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

using namespace std;

#define CENTIMETERS_IN_INCH 2.54
#define POUNDS_IN_KILOGRAM 2.2

// round result
double round(double d) {
   return floor(d + 0.5);
}

// round and truncate to 1 decimal place
double truncate(double d) {
   return round(double * 10) / 10;
}

int main() {
...
}