在一個程序中使用do-while循環

Question

該程序應該獲得用戶輸入（x）的任何數字的倍數，直到達到（y）。所有三個循環都能正常工作，但是當一起使用時，我們會得到前兩個循環，但第三個循環不會輸出。此外，我想要輸出每個循環的輸出在一個新的行。我的問題是我能做些什麼來使我的輸出分成三行，爲什麼不是我的第三個循環輸出任何東西。

#include <iostream> 
#include <string> 
#include <cstdlib> 
using namespace std; 

bool error(const string & msg); 

int main(){ 
    unsigned x, y; 
    cout << "Give me a number you want the multiples of and give me the max limit: "; 
    cin >> x >> y || error("Input Failure: "); 
    if (x == 0) error("Input can't be 0"); 

    unsigned increment = x; 
    x = 0; 

    while(x < y) 
    { 
     cout << x << ", "; 
     x += increment; 
     if (x > y) break; 
} 
    cout << endl; // This was the other problem. I kept putting it inside the loop 
    for(int x; x < y; x += increment){ 
     cout << x << ", "; 
     if (x > y) break; 
    } 

    cout << endl; // This was the other problem. I kept putting it inside the loop 
    x = 0; // This is what originally was wrong 
    do{ 
     cout << x << ", "; 
     x += increment; 
     if (x > y){ 
      break; 
     } 

    }while (x < y); 

} 

bool error(const string & msg){ 
     cout <<"Fatal error: " << msg << endl; 
     exit(EXIT_FAILURE); 
} 

Answer 1

好吧，這並不奇怪。當您單獨運行第三個循環時，變量x不會被其他兩個循環修改。實際上，你的第三個循環正在執行。第一個循環打印0,5，...，35，然後第二個循環打印0,5，...，35（注意for循環的條件中的<），第40個循環打印第三個循環，然後在它打印之後，while的條件是false，因爲40 == 40並且循環結束。

Answer 2

unsigned increment = x; 
x = 0; 

while(x < y) 
{ 
    cout << x << ", "; 
    x += increment; 
    if (x > y) break; 
} 

for(x = 0; x < y; x += increment){ 
    cout << x << ", "; 
    if (x > y) break; 
} 
x=0; 
do{ 
    cout << x << ", "; 
    x += increment; 
    if (x > y){ 
     break; 
    } 

}while (x < y); 

Answer 3

for循環不會輸出，因爲你重新定義x並沒有給它一個新的價值。我不確定爲什麼你使用三個循環，幾乎做同樣的事情，除非你只是好奇他們是如何工作的。例如，你可以做這樣的事情，用不同的循環輸出相同的東西：

#include <iostream> 
using namespace std; 

int main() 
{ 
    unsigned counter, increment, limit; 

    cout << "Give me a number you want to increment by of and give me the max limit: "; 
    cin >> increment >> limit; 

    //Check to see if the input stream failed 
    if(cin.fail()) 
    { 
     cout << "Fatal Error: Input Failure" << endl; 
     return -1; 
    } 

    if(increment == 0 || limit == 0) 
    { 
     cout << "Input Cannot Be 0" << endl; 
     return -1; 
    } 

    if(limit <= increment) 
    { 
     cout << "Limit <= Increment" << endl; 
     return -1; 
    } 

    cout << "First Loop" << endl; 
    counter = 0; //Set counter to 0 for 1st loop 
    while(counter <= limit) 
    { 
     cout << counter << ", "; 
     counter += increment; 
    } 
    cout << endl; 

    cout << "Second Loop" << endl; 
    //for loop resets counter for 2nd loop 
    for(counter = 0; counter <= limit; counter += increment) 
    { 
     cout << counter << ", "; 
    } 
    cout << endl; 

    cout << "Third Loop" << endl; 
    //Reset counter again for 3rd loop 
    counter = 0; 
    do{ 
     cout << counter << ", "; 
     counter += increment; 
    }while (counter <= limit); 

    return 0; 
}