While loop with tables C

Question

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#define N 30
int main()
{  char c, y, input[N];
int X, i=0, j;
printf("Give displacement\n");
scanf("%d",&X);
printf("Give chars\n");

while(((c=getchar()) !=EOF) && (i<N-1)){
    input[i]=c;
    i++;

}
input[i]='\0';
j=0;
for(j=0; j<=i-1; j++){
    if (isalpha(input[j])){
        if (isupper(input[j]))
          y=(input[j]-'A'+X)%26+'A';
        else
          y=(input[j]-'a'+X)%26+'A';
        putchar(y);
    }


}
return 0;
}

hey all. well, this code doesnt seems to works as it should. It skips 2 positions at the table instead of one. Which makes the program unusable since i need a table of 30 positions. I think that the problem is in the while loop, but i really cant find it. Any help would be apprecieted. Thanks in advance.

Answer 1

After the call to scanf , there's a newline left in the input buffer. That newline becomes the first character read by getchar .

To get the newline out of the buffer, add a separate call to getchar right after the scanf call:

scanf("%d",&X);
getchar();

That will give you the additional character you're missing.

Also, as mentioned in the comments, c should be defined as an int instead of a char , because getchar returns an int . Otherwise, the test for EOF will always be false.

Answer 2

if you want 30 characters you have to define N as 31

[0 - 29] + '\\0'

In your first while loop i believe that the second test is wrong:

Use it like this:

while(((c=getchar()) !=EOF) && (i<=N-1)){
    input[i]=c;
    i++;
}