character array blanking in c

问题:

code

int main()
{
     int n,m,i,j;char a[10][10];
     printf("enter n and m values\n");     
     scanf("%d%d",&n,&m);

     printf("enter array values");    
     for(i=0;i<n;i++)
        for(j=0;j<m;j++)
          scanf("%c",&a[i][j]);

     printf("the array is \n");
     for(i=0;i<n;i++)
        for(j=0;j<m;j++)
          printf("%d %d %c\t",i,j,a[i][j]);
}

Input

 Enter n and m values  
 4 5
 Enter characters 
 11111000001111100000

Output

0 0 

0 1 1   0 2 1   0 3 1   0 4 1   1 0 1   1 1 0   1 2 0   1 3 0   1 4 0   2 0 0    
2 1 1   2 2 1   2 3 1   2 4 1   3 0 1   3 1 0   3 2 0   3 3 0   3 4 0   

Error

If I give the value of n as 4 and m as 5 ,scanf does it job.

But while printing when the value of i is 0 and j is 0 it does not print anything.

Meanwhile a[0][1] prints the first input and a[0][2] prints second input and consecutively , so last input 0 is missing while printing.

Please explain why a[0][0] is avoided.

回答1:

Previous scanf calls leave behind \n character in the input buffer which goes along with input on pressing Enter or Return key. scanf("%c",&a[i][j]); reads that \n on first iteration.

You need to flush your input buffer. Either place a space before %c in scanf

scanf(" %c", &a[i][j]);   
       ^A space before `%c` can skip any number of leading white-spaces

or you can use

int c;
while((c = getchar()) != '\n' && c != EOF);  

---

NOTE: Will fflush(stdin) work in this case?

fflush is defined only for output streams. Since its definition of "flush" is to complete the writing of buffered characters (not to discard them), discarding unread input would not be an analogous meaning for fflush on input streams.

Suggested reading: c-faq 12.18.