a simple and fundamental question about scanf.

gaohua97115

printf("\nEnter a value: "); /* Prompt for the next value */
scanf(" %lf", &value);       /* Read the next value       */
total += value;              /* Add value to total        */
++count;                     /* Increment count of values */

question is:

why put a space before the %lf in scanf? only if put the space this part can be executed correctly.

thanks

emacsnw

No, you do not need this extra space.

argstormsky

不需要的, 就像你不需要用英文发贴一样.

zxgang_andy

funny。。。

gaohua97115

sorry about this. I did not install Scim.

If we do not enter the space, we will not see scanf is waiting for your input.  Very strange problem. The header ctype.h is included besides stdio.h.

BTW, i use the eclipse to build.

fnems

why, scanf is but always a blocking function

gaohua97115

This is a example from <<Beginning C From Novice to Professional>> ( Fourth Edition)

/* Program 4.6 The almost indefinite loop - computing an average */
#include <stdio.h>
#include <ctype.h>           /* For tolower() function */
int main(void)
{
  char answer = 'N';        /* Records yes or no to continue the loop */
  double total = 0.0;       /* Total of values entered                */
  double value = 0.0;       /* Value entered                          */
  int count = 0;            /* Number of values entered               */
  printf("\nThis program calculates the average of"
                                      " any number of values.");
  for( ;; )                           /* Indefinite loop */
  {
    printf("\nEnter a value: ");      /* Prompt for the next value */
    scanf(" %lf", &value);            /* Read the next value       */
    total += value;                   /* Add value to total        */
    ++count;                          /* Increment count of values */
    /* check for more input */
    printf("Do you want to enter another value? (Y or N): ");
    scanf(" %c", &answer);            /* Read response Y or N   */
    if(tolower(answer) == 'n')        /* look for any sign of no */
      break;                          /* Exit from the loop      */
  }
  /* output the average to 2 decimal places */
  printf("\nThe average is %.2lf\n", total/count );
  return 0;
}


try this program with and without that space. you will see the difference.

thanks.

argstormsky

原来是没装输入法, 囧.


scanf(" %lf", &value);            /* Read the next value       */

注意这行, 你前面加了一个空格, 那么你的输入就要按照你的格式字符串的形式来输入.

如果是
scanf("%d,%d", &a, &b);  那么你的输入也以逗号隔开.