我正在开展一个学校项目，在这个项目中，我应该采用各种“FIXME”部分，并将它们提供给主要功能之外的功能。我以为我把一切都搞定了，然后什么都没有用。我重新开始，我把它缩小到导致问题的功能。我将在下面的代码中标记它。也就是说，我可以轻松地将其格式化为函数，并且我的函数语法是正确的答案，但是如果我在函数中有东西而不是函数则完全不同。这是没有函数的代码：
#include <iostream>
#include <iomanip>
#include <cmath>
#include <cstdlib>
#include <ctime>
using namespace std;
const double pi = 3.14159265;
const double grav = 9.8; // Earth gravity (m/s^2)
// Given time, angle, velocity, and gravity
// Update x and y values
void Trajectory(double t, double a, double v,
double& x, double& y) {
x = v * t * cos(a);
y = v * t * sin(a) - 0.5 * grav * t * t;
return;
}
// convert degree value to radians
double DegToRad(double deg) {
return ((deg * pi) / 180.0);
}
// print time, x, and y values
void PrintUpdate(double t, double x, double y) {
cout << "Time " << fixed << setprecision(0)
<< setw(3) << t << " x = " << setw(3)
<< x << " y = " << setw(3) << y << endl;
return;
}
void PrintIntro() { //This function is going to print the intro to the game!
cout << "Welcome to Upset Fowl!\n";
cout << "The objective is to hit the Mean Swine by launching an Upset Fowl.\n";
}
int main() {
double t = 1.0; // time (s)
double fowlY = 0.0; // object's height above ground (m)
double fowlAngle = 0.0; // angle of launch of fowl (rad)
double fowlVel = 0.0; // velocity of fowl (m/s)
double fowlX = 0.0; // object's horiz. dist. from start (m)
double fowlLandingX = 0.0; // fowl’s horiz. dist. from start (m)
double swineX = 0.0; // distance to swine (m)
double beforeSwineX = 0.0; // distance before swine that is acceptable as a hit (m)
bool didHitSwine = false; // did hit the swine?
srand(time(0));
swineX = 50; //(rand() % 201) + 50; I took out the randomness so I can keep track of answers easily.
PrintIntro();
cout << "\nThe Mean Swine is " << swineX << " meters away.\n";
cout << "Enter fowl launch angle (deg): ";
cin >> fowlAngle;
fowlAngle = ((fowlAngle * pi) / 180.0); // convert to radians
cout << "Enter fowl launch velocity (m/s): ";
cin >> fowlVel;
// FIXME Make into a function called LaunchFaowl
do {
PrintUpdate(t, fowlX, fowlY);
Trajectory(t, fowlAngle, fowlVel, fowlX, fowlY);
t = t + 1.0;
} while (fowlY > 0.0); // while above ground
PrintUpdate(t, fowlX, fowlY);
fowlLandingX = fowlX;
// FIXME Make into a function called DtrmnIfHit
beforeSwineX = swineX - 30;
if ((fowlLandingX <= swineX) && (fowlLandingX >= beforeSwineX)) {
cout << "Hit'em!!!" << endl;
didHitSwine = true;
}
else {
cout << "Missed'em..." << endl;
didHitSwine = false;
}
return 0;
}
以下是具有以下功能的代码：
#include <iostream>
#include <iomanip>
#include <cmath>
#include <cstdlib>
#include <ctime>
using namespace std;
const double pi = 3.14159265;
const double grav = 9.8; // Earth gravity (m/s^2)
// Given time, angle, velocity, and gravity
// Update x and y values
void Trajectory(double t, double a, double v,
double& x, double& y) {
x = v * t * cos(a);
y = v * t * sin(a) - 0.5 * grav * t * t;
return;
}
// convert degree value to radians
double DegToRad(double deg) {
return ((deg * pi) / 180.0);
}
// print time, x, and y values
void PrintUpdate(double t, double x, double y) {
cout << "Time " << fixed << setprecision(0)
<< setw(3) << t << " x = " << setw(3)
<< x << " y = " << setw(3) << y << endl;
return;
}
void PrintIntro() { //This function is going to print the intro to the game!
cout << "Welcome to Upset Fowl!\n";
cout << "The objective is to hit the Mean Swine by launching an Upset Fowl.\n";
}
void GetUsrInpt(double piggy, double slope, double Velocity) { // FIXME Make into a function called GetUsrInpt
cout << "\nThe Mean Swine is " << piggy << " meters away.\n";
cout << "Enter fowl launch angle (deg): ";
cin >> slope;
slope = ((slope * pi) / 180.0); // convert to radians
cout << "Enter fowl launch velocity (m/s): ";
cin >> Velocity;
}
int main() {
double t = 1.0; // time (s)
double fowlY = 0.0; // object's height above ground (m)
double fowlAngle = 0.0; // angle of launch of fowl (rad)
double fowlVel = 0.0; // velocity of fowl (m/s)
double fowlX = 0.0; // object's horiz. dist. from start (m)
double fowlLandingX = 0.0; // fowl’s horiz. dist. from start (m)
double swineX = 0.0; // distance to swine (m)
double beforeSwineX = 0.0; // distance before swine that is acceptable as a hit (m)
bool didHitSwine = false; // did hit the swine?
srand(time(0));
swineX = 50; //(rand() % 201) + 50;
PrintIntro();
GetUsrInpt(swineX, fowlAngle, fowlVel);
// FIXME Make into a function called LaunchFaowl
do {
PrintUpdate(t, fowlX, fowlY);
Trajectory(t, fowlAngle, fowlVel, fowlX, fowlY);
t = t + 1.0;
} while (fowlY > 0.0); // while above ground
PrintUpdate(t, fowlX, fowlY);
fowlLandingX = fowlX;
// FIXME Make into a function called DtrmnIfHit
beforeSwineX = swineX - 30;
if ((fowlLandingX <= swineX) && (fowlLandingX >= beforeSwineX)) {
cout << "Hit'em!!!" << endl;
didHitSwine = true;
}
else {
cout << "Missed'em..." << endl;
didHitSwine = false;
}
return 0;
}
现在，我问的是这些节目在哪里误入歧途？我找不到任何理由，我搜索了所有变量，并且认为它们不应该是一个问题。我该如何解决？
注意：我不希望别人为我处理所有FIXME部分！我只是想知道我哪里出错了所以我可以照顾其余的人。
答案 0 :(得分：0)
斜率必须通过引用传递：
void GetUsrInpt(double piggy, double& slope, double Velocity) { // FIXME Make into a function called GetUsrInpt
cout << "\nThe Mean Swine is " << piggy << " meters away.\n";
cout << "Enter fowl launch angle (deg): ";
cin >> slope;
slope = ((slope * pi) / 180.0); // convert to radians
cout << "Enter fowl launch velocity (m/s): ";
cin >> Velocity;
}
如果希望在函数中传递的变量中实际更改参数的值，则必须将其作为指针传递（传统上在C中）或在函数原型中将其声明为参考传递的参数（C ++） ）如上所述。
你的教授通过参考x和y来改变函数内的变化：＆amp; x＆amp; y
void Trajectory(double t, double a, double v,
double& x, double& y) {
x = v * t * cos(a);
y = v * t * sin(a) - 0.5 * grav * t * t;
return;
}
对于在函数中更改其值的其他变量，以相同的方式工作，您将完成它。
答案 1 :(得分：0)
您已设置函数GetUsrInpt以将双参数传递为＆gt;“按值传递”，因此只将swineX，＆gt; fowlAngle和fowlVel的值的副本传递给函数。在＆gt;函数中更改它们不会更改main函数中的值。如果你想＆gt;更改它们并让主函数知道它，你必须通过使用指向变量的指针来传递＆gt;引用。 像这样
void GetUsrInpt(double* ptrPiggy, double* pSlope, double* pVelocity)
{
//...
cin >> *pPiggy;
cin >> *pSlope;
cin >> *pVelocity;
//...
}
//像这样调用函数：
GetUsrInpt( &swineX, &fowlAngle, &fowlVel );