如果我的循環中的語句被跳過C

Question

在函數verify中，我有一個稱爲「size」的循環，它與「foodSelect」中的第3個循環相同，只是它由於某種原因工作不同。它不會首先提示我輸入，它會直接轉到if內部，並詢問What size (L - Large, M - Medium, S - Small): Please enter S, M, or L only:。它首先顯示錯誤，然後再次提示我輸入。有點奇怪。

源（因爲它是長）：http://pastebin.com/raw.php?i=KxrMAXaU

或源位置：

#include <stdio.h> 
#include <string.h> 

void menu(); 
void question (char choice[]); 
void output(char *foodChoice, char *foodSelect, char *foodSize, int *foodOrderNum, float *foodSubtotal); 
int verify(char *choice, char *foodChoice); 

void menu() { 
/* 
printf("\n"); 
*/ 
    printf("\nWelcome to Sunny FISH & CHIPS!\n\n"); 
    printf("########  Fish :  Haddock(K) Large(L) | $5.00\n"); 
    printf("# FOOD #    Halibut(T) Large(L) | $4.00\n"); 
    printf("########  Chips:  Cut(C)  Large(L) | $2.00\n"); 
    printf("      Ring(R) Large(L) | $3.00\n"); 
    printf("           | \n"); 
    printf("########## Soft Drinks(S)  Large(L) | $2.00\n"); 
    printf("# DRINKS # Coffee(C)    Large(L) | $1.75\n"); 
    printf("########## Tea(T)    Large(L) | $1.50\n"); 
    printf("---------------------------------------------\n"); 
    printf("Note: Medium price: 80%% of large.\n"); 
    printf("  Small price: 60%% of large.\n"); 
    printf("TAX is 10%%.\n"); 
    printf("More than 5 fish, 10%% discount on drink.\n"); 
    printf("Every 10 fish purchased, get 1 free softdrink.\n"); 
    printf(" - size of drink is according to size of fish\n"); 
    printf("----------------------------------------------\n\n"); 
} 

int verify(char *choice, char *foodChoice) 
{ 
    int answer, rc = -1; 
    if (choice == "order") 
    { 
     do { 
      answer = getchar(); 
      if (answer == 'Y' || answer == 'y') 
      { rc = 1; } 
      else if (answer == 'N' || answer == 'n') 
      { rc = 0; } 
      if (rc == -1 && answer != -1) 
      { 
       printf("Please enter y or n only: "); 
       while (answer != -1 && answer != '\n') 
       answer = getchar(); 
      } 
     } while (rc == -1 && answer != -1); 
    } 
    if (choice == "foodSelect") 
    { 
     do { 
      answer = getchar(); 

       if (foodChoice == "Fish") 
       { 
        do { 
         answer = getchar(); 
         if (answer == 'K' || answer == 'k') 
         { rc = 1; } 
         else if (answer == 'T' || answer == 't') 
         { rc = 0; } 
         if (rc == -1 && answer != -1) 
         { 
          printf("Please enter K or T only: "); 
          while (answer != -1 && answer != '\n') 
          answer = getchar(); 
         } 
        } while (rc == -1 && answer != -1); 
       } 
       if (foodChoice == "Chips") 
       { 
        do { 
         answer = getchar(); 
         if (answer == 'C' || answer == 'c') 
         { rc = 1; } 
         else if (answer == 'R' || answer == 'r') 
         { rc = 0; } 
         if (rc == -1 && answer != -1) 
         { 
          printf("Please enter C or R only: "); 
          while (answer != -1 && answer != '\n') 
          answer = getchar(); 
         } 
        } while (rc == -1 && answer != -1); 
       } 
       if (foodChoice == "Drinks") 
       { 
        do { 
         answer = getchar(); 
         if (answer == 'S' || answer == 's') 
         { rc = 1; } 
         else if (answer == 'C' || answer == 'c') 
         { rc = 2; } 
         else if (answer == 'T' || answer == 'T') 
         { rc = 3; } 
         if (rc == -1 && answer != -1) 
         { 
          printf("Please enter S, C, or T only: "); 
          while (answer != -1 && answer != '\n') 
          answer = getchar(); 
         } 
        } while (rc == -1 && answer != -1); 
       } 
     } while (rc == -1 && answer != -1); 
    } 
    if (choice == "size") 
    { 
     do { 
      answer = getchar(); 
      if (answer == 'S' || answer == 's') 
      { rc = 1; } 
      else if (answer == 'M' || answer == 'm') 
      { rc = 2; } 
      else if (answer == 'L' || answer == 'l') 
      { rc = 3; } 
      if (rc == -1 && answer != -1) 
      { 
       printf("Please enter S, M, or L only: "); 
       while (answer != -1 && answer != '\n') 
       answer = getchar(); 
      } 
     } while (rc == -1 && answer != -1); 
    } 
} 

void question (char *choice) { 

    char *choiceYesNo; 
    char *foodOptions; 
    char *foodChoice; 
    char *foodSelect; 
    char *foodSize; 
    int *foodOrderNum; 
    float *foodSubtotal; 

    switch (choice[0]) { 
     case 'f': 
      foodChoice = "Fish"; 
      foodOptions = "(K- Haddock, T- Halibut)"; 
      break; 
     case 'c': 
      foodChoice = "Chips"; 
      foodOptions = "(C- Cut, R- Ring)"; 
      break; 
     case 'd': 
      foodChoice = "Drinks"; 
      foodOptions = "(S- Softdrink, C- Coffee, T- Tea)"; 
      break; 
    } 

    printf("\nDo you order %s? (Y/N): ", foodChoice); 
     verify("order", foodChoice); 
    printf("%s choice %s: ", foodChoice, foodOptions); 
     verify("foodSelect", foodChoice); 
    printf("What size (L - Large, M - Medium, S - Small): "); 
     verify("size", foodChoice); 
    printf("How many orders do you want? (>=0): "); 
     scanf("%d", &foodOrderNum); 
    output(foodChoice, foodSelect, foodSize, foodOrderNum, foodSubtotal); 
} 

void output(char *foodChoice, char *foodSelect, char *foodSize, int *foodOrderNum, float *foodSubtotal) { 

    printf("\nYou ordered %s: %c - SIZE: %c amount ordered: %d, subtotal price: %.2lf\n\n", 
    foodChoice, foodSelect, foodSize, foodOrderNum, foodSubtotal); 

} 



int main() { 

    //menu(); 

    question("drinks"); 


} 

Answer 1

除了你實際上不應該將字符串與==進行比較（儘管在這種情況下，由於只使用字符串文本而不太可能工作），但是您的麻煩是因爲需要輸入選項返回鍵被按下。因此，當您從輸入緩衝區中獲取一個字符作爲選擇時，仍然存在一個換行符。放置一個

printf("answer = %d\n",answer); 

之後的第一個answer = getchar();在循環中。這將告訴你，你已經從輸入緩衝區獲得換行'\n'（10）[或者可能是回車'\r'（13），但是因爲以下原因，我認爲情況並非如此]。在foodSelect循環中，if語句之前有一個answer = getchar();，並且在do-while循環的開始處有一個answer = getchar();，這樣就清除了輸入緩衝區。但在foodSize分支你沒有。

每個選擇後，清除輸入緩衝器

while((answer = getchar()) != -1 && answer != '\n); 

Answer 2

我不建議使用getchar()的互動節目。您似乎無法處理您輸入的所有內容後將出現的換行符。改爲使用fgets()。

爲了澄清上述情況，當你按下喜歡Ÿ東西進入，你已經進入字符到標準輸入。第一次撥打電話getchar()，將返回'Y'，下一個電話將返回'\n'（換行符）。您的代碼不希望出現以下換行符，並且可能會顯示「跳過」getchar()的調用，但實際上它正在返回更多您輸入的字符。

如果您使用fgets()，那麼您將獲得整個用戶輸入的整行，包括換行符，全部一次。您（通常）不必擔心在輸入緩衝區中等待的額外數據。

Answer 3

您無法將字符串與==進行比較。由於字符串本質上是指針（指向字符數組），因此您正在比較指針（存儲字符的內存中的實際地址）。爲了逐字符比較字符串，您需要使用適當的函數，缺省選項是strcmp。

另外，正如Greg Hewgill所說，如果您使用getchar，您將會看到您的問題中描述的跳過行爲。原因是爲了讓用戶從getchar（）控制回代碼，他們需要按enter（這是控制檯輸入的工作方式）。密鑰enter將是所讀取的字符之一（即如果用戶輸入「y」則爲第二個字符），所以當getchar返回enter密鑰的密碼時，字符的比較也會失敗。