简单C ++错误：“...未声明（首先使用此函数） [英] Simple C++ Error: "... undeclared (first use this function)"

问题描述

我正在开始我的第一个C ++程序。由于某种原因，当我尝试编译它时，我得到以下错误：

 `truncate'undeclared（首先使用此函数） 
  

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，cm，weight_in_kg，weight_in_lbs; 
 
 //获取以英尺和英寸为单位的高度
 cout< 输入高度（英尺）：; 
 cin>>英尺
 cout<< Enter（inches）：; 
 cin>>英寸; 
 
 //将英尺和英寸转换为厘米
厘米=（（12 *英尺）+英寸）* CENTIMETERS_IN_INCH; 
 
 // round 2个小数位和truncate 
厘米= truncate（厘米）; 
 
 printf（有人是％g'％g \将是％g cm tall，英尺，英寸，厘米）; 
 
 // bmi的权重of 18.5 
 weight_in_kg = truncate（18.5 * centimeters）; 
 weight_in_lbs = round（weight_in_kg * POUNDS_IN_KILOGRAM）; 
 
 printf（18.5 BMI对应于约％g kg或％ g lb，weight_in_kg，weight_in_lbs）; 
 
 // bmi的权重为25 
 weight_in_kg = truncate（25 * cimeters）; 
 weight_in_lbs = round（weight_in_kg * POUNDS_IN_KILOGRAM）; 
 
 printf（25.0 BMI将对应于约％g kg或％g lbs，weight_in_kg，weight_in_lbs）; 
 
 //暂停输出
 cin> > feet; 
 
 return 0; 
} 
 
 // round result 
 double round（double d）{
 return floor d + 0.5）; 
} 
 
 //舍入到小数点后1位
 double truncate（double d）{
 return round（double * 10） 10; 
} 
  

任何帮助将不胜感激。

p>

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

您可以在main之前定义函数，这将解决问题：

  #include< iostream> 
 #include< math.h> 
 
 using namespace std; 
 
 #define CENTIMETERS_IN_INCH 2.54 
 #define POUNDS_IN_KILOGRAM 2.2 
 
 //舍入结果
双回合（双d）{
回到楼层d + 0.5）; 
} 
 
 //舍入和截断到小数点后一位
 double truncate（double d）{
 return round（double * 10）/ 10; 
} 
 
 int main（）{
 ... 
} 
  

Hey guys, I am working on my first C++ program for school. For some reason I am getting the following error when I try to compile it:

`truncate' undeclared (first use this function)

Full Source:

#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;
}

Any help would be appreciated. Thanks.

解决方案

You need forward declaration before your main:

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

You could just define your functions before main, that will solve the problem too:

#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() {
...
}

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