程序不會在第二個scanf（）讀取（）

Question

我不明白我出錯的地方。它不會在第二個scanf()只讀跳到下一行。

#include <stdio.h> 
#define PI 3.14 

int main() 
{ 
    int y='y', choice,radius; 
    char read_y; 
    float area, circum; 

do_again: 
    printf("Enter the radius for the circle to calculate area and circumfrence \n"); 
    scanf("%d",&radius); 
    area = (float)radius*(float)radius*PI; 
    circum = 2*(float)radius*PI; 

    printf("The radius of the circle is %d for which the area is %8.4f and circumfrence is %8.4f \n", radius, area, circum); 

    printf("Please enter 'y' if you want to do another calculation\n"); 
    scanf ("%c",&read_y); 
    choice=read_y; 
    if (choice==y) 
     goto do_again; 
    else 
     printf("good bye"); 
    return 0; 
} 

Answer 1

您的第一個scanf（）在輸入流中留下了一個換行符，當您讀取一個char時，它會被下一個scanf（）使用。

變化

scanf ("%c",&read_y); 

到

scanf (" %c",&read_y); // Notice the whitespace 

這會忽略所有空格。

---

通常，避免scanf（）讀取輸入（特別是在混合不同格式時）。請使用fgets()並使用sscanf()解析它。

Answer 2

，你可以這樣做：

#include <stdlib.h> 
#define PI 3.14 

void clear_buffer(void); 

int main() 
{ 
    int y='y',choice,radius; 
    char read_y; 
    float area, circum; 
    do_again: 
     printf("Enter the radius for the circle to calculate area and circumfrence \n");   
     scanf("%d",&radius);   
     area = (float)radius*(float)radius*PI; 
     circum = 2*(float)radius*PI;  
     printf("The radius of the circle is %d for which the area is %8.4f and circumfrence is %8.4f \n", radius, area, circum); 
     printf("Please enter 'y' if you want to do another calculation\n"); 
     clear_buffer(); 
     scanf("%c",&read_y);    
     choice=read_y;  
    if (choice==y) 
     goto do_again; 
    else 
     printf("good bye\n"); 
    return 0; 
} 

void clear_buffer(void) 
{ 
    int ch; 

    while((ch = getchar()) != '\n' && ch != EOF); 
} 

，或者你可以scanf函數之前寫fflush（STDIN）