我的簡單代碼沒有給出輸出

Question

#include <stdio.h> 
#include <conio.h> 
int main(void) 
{ 
    int year; 
    float principal, amount, inrate, period, value; 
    printf ("Please enter principal"); 
    scanf ("%f", principal); 
    amount = principal; 
    printf ("Please enter interest rate"); 
    scanf ("%f", inrate); 
    year = 0; 
    printf ("Please enter period"); 
    scanf ("%f", period); 
     while(year <= period) 
      {printf ("%d %f\n", year, amount); 
      value = amount + amount*inrate; 
      year = year + 1; 
      amount = value; 
      } 
     getch(); 
    return 0; 
} 

我試着運行這段代碼，但是我根本沒有輸出。有0個警告和消息。坦率地說，我不知道代碼是否能夠達到預期的目的而不能運行它！請幫忙。

Answer 1

您遇到的問題是雙重的。第一個，scanf需要一個指針來存儲值。 （例如scanf ("%f", principal);應該scanf ("%f", &principal);）

另一個問題需要注意的是讀值隨scanf每次按[Enter]時會留下一個換行符'\n'輸入緩衝區stdin。 scanf會讀取您輸入的號碼，但將換行符保留在stdin。下次您撥打scanf時，它會在stdin中看到換行符（值：0xa十六進制，10），並將其作爲下一個值讀取。

注意：在這種情況下，%f將跳過換行，所以這是沒有必要的。但是，請注意，由scanf讀取的小數或字符串將會生效。在使用scanf時請始終記住這一點。

如果遇到scanf似乎會跳過預期的輸入，一個簡單的解決方案是清空（空）輸入緩衝區。 （下面的函數flush_stdin提供瞭如何處理這個問題的一個例子）。在每次致電scanf後，請致電flush_stdin，這是潛在的問題。

#include <stdio.h> 
// #include <conio.h> 

void flush_stdin() 
{ 
    int c = 0; 
    while ((c = getchar()) != '\n' && c != EOF); 
} 

int main(void) 
{ 
    int year = 0; /* Always INITIALIZE your variables */ 
    float principal, amount, inrate, period, value; 
    principal = amount = inrate = period = value = 0; 

    printf ("Please enter principal: "); 
    scanf ("%f", &principal); 

    amount = principal; 

    printf ("Please enter interest rate: "); 
    scanf ("%f", &inrate); 

    year = 0; 

    printf ("Please enter period: "); 
    scanf ("%f", &period); 

    while(year <= period) 
    { 
     printf ("%3d %10.2f\n", year, amount); 
     value = amount + amount*inrate; 
     year = year + 1; 
     amount = value; 
    } 

    // getch(); 

    return 0; 
} 

輸出

$ ./bin/scanf_noop 
Please enter principal: 123.45 
Please enter interest rate: .05 
Please enter period: 24 
    0  123.45 
    1  129.62 
    2  136.10 
    3  142.91 
    4  150.05 
    5  157.56 
    6  165.43 
    7  173.71 
    8  182.39 
    9  191.51 
10  201.09 
11  211.14 
12  221.70 
13  232.78 
14  244.42 
15  256.64 
16  269.48 
17  282.95 
18  297.10 
19  311.95 
20  327.55 
21  343.93 
22  361.12 
23  379.18 
24  398.14 

Answer 2

scanf從標準輸入讀取數據，並根據參數格式將它們存儲到附加參數指向的位置。所以如果你想用scanf在變量中保存一些東西，你應該把指針作爲參數與&。

Answer 3

在scanf()調用中的可變參數之前添加&地址之後，它可以工作。但我沒有檢查算術。

#include <stdio.h> 
#include <conio.h> 

int main(void) 
{ 
    int year; 
    float principal, amount, inrate, period, value; 
    printf ("Please enter principal "); 
    scanf ("%f", &principal);     // <-- added & 
    amount = principal; 
    printf ("Please enter interest rate "); 
    scanf ("%f", &inrate);      // <-- added & 
    year = 0; 
    printf ("Please enter period "); 
    scanf ("%f", &period);      // <-- added & 
    while(year <= period) { 
     printf ("%d %f\n", year, amount); 
     value = amount + amount*inrate; 
     year = year + 1; 
     amount = value; 
    } 
    getch(); 
    return 0; 

}

Answer 4

我嘗試運行此代碼，但我必須在所有

真的沒有輸出？我有6個警告和段錯誤！你在用什麼編譯器？

 ||=== Build: Debug in test (compiler: GNU GCC Compiler) ===| 
     main.cpp||In function 'int main()':| 
     main.cpp|8|warning: format '%f' expects argument of type 'float*', but argument 2 has type 'double' [-Wformat]| 
     main.cpp|11|warning: format '%f' expects argument of type 'float*', but argument 2 has type 'double' [-Wformat]| 
     main.cpp|14|warning: format '%f' expects argument of type 'float*', but argument 2 has type 'double' [-Wformat]| 
     main.cpp|8|warning: 'principal' is used uninitialized in this function [-Wuninitialized]| 
     main.cpp|11|warning: 'inrate' is used uninitialized in this function [-Wuninitialized]| 
     main.cpp|14|warning: 'period' is used uninitialized in this function [-Wuninitialized]| 
     ||=== Build finished: 0 error(s), 6 warning(s) (0 minute(s), 0 second(s)) ===| 

代碼看起來像某種利益計算器（https://en.wikipedia.org/wiki/Interest）

嘗試代碼：

#include <stdio.h> 
    #include <conio.h> 
    int main(void) 
    { 
     int year; 
     float principal, amount, inrate, period, value; 
     printf ("Please enter principal "); 
     scanf ("%f", &principal); 
     amount = principal; 
     printf ("Please enter interest rate "); 
     scanf ("%f", &inrate); 
     year = 0; 
     printf ("Please enter period "); 
     scanf ("%f", &period); 
      while(year <= period) 
       { 
       printf ("%d %f\n", year, amount); 
       value = amount + amount*inrate; 
       year = year + 1; 
       amount = value; 
       } 
      getch(); 
     return 0; 
    }