当用户没有输入数字时，我得到一个无限循环。我已经尝试了几个小时而且无法让它停下来我是新手，所以如果你能帮我停止无限循环，我会感激不尽。无限循环似乎只发生在用户输入非数字的东西时。
// libraries to add that are required for this program with
// identification of what library gives what objects
#include <iostream> // provides: cout, cin
#include <iomanip> // provides: setw setprecision(n)
#include <limits>
// setting up the environment
using namespace std;
int main()
{
// usimg Window.h
// Print out title of program
cout << " - GPA Calculation Program - \n";
string str; // Gets User inpit
// Give 2 lines spacing
cout << endl;
cout << endl;
// list of variables needed
const double max = 100; // constant variable for max grade = 100
const double min = 0; // constant variable for min grade = 0
const double Hours = 3; // constant variable for Credit Hours = 3
int gradeNum = 0; // variable for Grade #
double grade; // variable for Grade input by user
double GPA; // variable for value of GPA points varys by user inputs for grade
bool True1 = true; // bool statement for True
bool True2 = true; // bool statement for True
bool True3 = true; // bool statement for True
bool True4 = true; // bool statement for True
double Total = 0.0; // variable for adding all of the Total_GPA_multiply_HOURS together
double TotalGpa = 0.0; // variable for adding all of gpa together
double gpa = 0.0; // variable for value of GPA being incremented
double Total_GPA_multiply_HOURS = 0.0; // variable for value of results of GPA * Hours
// start a while loop Asking user for input and give them response
while (True1 == true)
{
gradeNum++; // Grade number is increased by 1 for each user entry
True4 = true; // Turn switch 4 on
while (True4 == true)
{ // start of 4th while loop
bool True2 = true; // bool statement for True
//Prints to the console the question the the user will answer with a number that represents their grade
cout << "Enter Grade " << gradeNum << " (From 0 to 100): ";
cin >> grade;
while (True2 == true)
{// start of 2nd while loop
if (grade >= 90 && grade <= max)
{ // start 1st if
// prints Letter grade for user input if statements true
// and does calculations to get the user GPA
cout << "Your letter grade is A \n";
GPA = 4;
gpa += 4;
Total_GPA_multiply_HOURS = GPA * Hours;
True2 = false;
True4 = false;
True3 = true;
True3 = true;
}
else if (grade >= 80 && grade <90)
{
// prints Letter grade for user input if statements true
// and does calculations to get the user GPA
cout << "Your letter grade is B \n";
GPA = 3;
gpa += 3;
Total_GPA_multiply_HOURS = GPA * Hours;
True2 = false;
True4 = false;
True3 = true;
True3 = true;
}
else if (grade >= 70 && grade <80)
{
// prints Letter grade for user input if statements true
// and does calculations to get the user GPA
cout << "Your letter grade is C \n\n";
GPA = 3;
gpa += 3;
Total_GPA_multiply_HOURS = GPA * Hours;
True2 = false;
True4 = false;
True3 = true;
True3 = true;
}
else if (grade >= 60 && grade <70)
{
// prints Letter grade for user input if statements true
// and does calculations to get the user GPA
cout << "Your letter grade is D \n\n";
GPA = 2;
gpa += 2;
Total_GPA_multiply_HOURS = GPA * Hours;
True2 = false;
True4 = false;
True3 = true;
True3 = true;
}
else if (grade >= min && grade <60)
{
// prints Letter grade for user input if statements true
// and does calculations to get the user GPA
cout << "Your letter grade is F \n\n";
GPA = 0;
gpa += 0;
Total_GPA_multiply_HOURS = GPA * Hours;
True2 = false;
True4 = false;
True3 = true;
True3 = true;
}
else if ((grade < min || grade > max) && (grade > -100000000 && grade < 100000000))
{
// print error for invalid entry
cout << "*** ERROR: " << grade << " is INVALID grade\n" << " Grade must be from 0 to 100! \n \n PLease enter a Grade and has to be from 0 to 100!\n\n\n";
True2 = false;
True4 = true;
}
else
{
// print error for invalid entry
cout << "*** ERROR: The input you have provided is not a number!\n Please enter a number from 1 to 100!\n\n\n";
cin.fail();
cin.clear();
cin.ignore(numeric_limits<streamsize>::max(), '\n');
True1 = false;
True2 = false;
True3 = false;
True4 = false;
} // end of 1st if
} // end of 2nd while loop
}// end 4th while loop
}// end 1st while loop
system("pause");
return 0;
}
答案 0 :(得分：0)
你说：
当用户没有输入数字时，我得到一个无限循环
创建一个打印提示的函数，尝试读取数字，如果读取不成功，则清除输入流并再次调用自身。
double readGrade(int gradeNum)
{
double grade;
cout << "Enter Grade " << gradeNum <<" (From 0 to 100): ";
if ( !(cin >> grade) )
{
// Clear the stream.
cin.clear();
// Discard everything up to the newline.
cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n');
// Call the function again.
return readGrade(gradeNum);
}
return grade;
}
然后，替换主
中的以下行cout << "Enter Grade " << gradeNum <<" (From 0 to 100): ";
cin >> grade;
致电readGrade()。
grade = readGrade(gradeNum);
答案 1 :(得分：0)
我已经在多个地方调整了你的GPA课程：
添加了2个变量以跟踪被视为输入的主题并设置最多10个主题。
int maxSubjects = 10;
int currentSubject = 0;
然后检查条件(currentSubject < maxSubjects)以确保
不超过科目数。
将计算从Total_GPA_multiply_HOURS = GPA * Hours;更改为Total_GPA_multiply_HOURS += GPA * Hours;，因为我们需要此值才能在输入所有值后获得人员的实际GPA。
在内部while循环之后添加了一个条件以确保外部while 输入10个科目时退出循环
if (currentSubject == maxSubjects){
break;
}
添加了一行以打印出计算出的GPA，cout << "GPA: " << (Total_GPA_multiply_HOURS/gpa) << endl;
这是完整的程序：
#include <iostream>
#include <iomanip>
#include <limits>
using namespace std;
int main()
{
cout << " - GPA Calculation Program -" << endl << endl << endl;
string str;
const double max = 100;
const double min = 0;
const double Hours = 3;
int maxSubjects = 10;
int currentSubject = 0;
int gradeNum = 0;
double grade;
double GPA;
bool True1 = true;
bool True2 = true;
bool True3 = true;
bool True4 = true;
double Total = 0.0;
double TotalGpa = 0.0;
double gpa = 0.0;
double Total_GPA_multiply_HOURS = 0.0;
while (True1 == true)
{
gradeNum++;
True4 = true;
currentSubject++;
while (True4 == true && (currentSubject < maxSubjects))
{
True2 = true;
cout << "Enter Grade " << gradeNum << " (From 0 to 100): ";
cin >> grade;
while (True2 == true)
{
if (grade >= 90 && grade <= max)
{
cout << "Your letter grade is A \n";
GPA = 4;
gpa += 4;
Total_GPA_multiply_HOURS += GPA * Hours;
True2 = false;
True4 = false;
True3 = true;
}
else if (grade >= 80 && grade <90)
{
cout << "Your letter grade is B \n";
GPA = 3;
gpa += 3;
Total_GPA_multiply_HOURS += GPA * Hours;
True2 = false;
True4 = false;
True3 = true;
}
else if (grade >= 70 && grade <80)
{
cout << "Your letter grade is C \n\n";
GPA = 3;
gpa += 3;
Total_GPA_multiply_HOURS += GPA * Hours;
True2 = false;
True4 = false;
True3 = true;
}
else if (grade >= 60 && grade <70)
{
cout << "Your letter grade is D \n\n";
GPA = 2;
gpa += 2;
Total_GPA_multiply_HOURS += GPA * Hours;
True2 = false;
True4 = false;
True3 = true;
}
else if (grade >= min && grade <60)
{
cout << "Your letter grade is F \n\n";
GPA = 0;
gpa += 0;
Total_GPA_multiply_HOURS += GPA * Hours;
True2 = false;
True4 = false;
True3 = true;
}
else if ((grade < min || grade > max) && (grade > -100000000 && grade < 100000000))
{
cout << "*** ERROR: " << grade << " is INVALID grade\n" << " Grade must be from 0 to 100! \n \n PLease enter a Grade and has to be from 0 to 100!\n\n\n";
True2 = false;
True4 = true;
}
else
{
cout << "*** ERROR: The input you have provided is not a number!\n Please enter a number from 1 to 100!\n\n\n";
cin.fail();
cin.clear();
cin.ignore(numeric_limits<streamsize>::max(), '\n');
True1 = false;
True2 = false;
True3 = false;
True4 = false;
}
}
}
if (currentSubject == maxSubjects){
break;
}
}
cout << "GPA: " << (Total_GPA_multiply_HOURS/gpa) << endl;
return 0;
}
希望这有帮助。