I' ve inserted the followings input for the follow program:
a b c d e
After the e letter I've pressed Enter, but the program blocks on scanf for i equal to 3. Seems that scanf is not able to fetch other character from stdin. Thanks in advance for your help.
#include <stdio.h>
#include <stdlib.h>
int main()
{
char a[5];
for (int i = 0; i < 5; i++)
{
scanf("%c ", a + i);
printf("i = %d a[%d] = %c \n", i, i, a[i]);
}
int i = 0;
while( i < 5 )
{
printf("%c ", a[i]);
i++;
}
return 0;
}
It doesn't block when i == 3 -- it completes that iteration -- it blocks when i == 4.
That's because of the space after the %c in the scanf format -- a space causes scanf to read input and skip whitespace up until it finds a non-whitespace character. That non-whitespace character will then be left in the FILE input buffer as the next character to be read. So in the 5th iteration of the loop (i == 4), it reads the e then reads whitespace looking for non-whitespace. So the newline is skipped over (it's whitespace) and it starts (trying to) read the next line which blocks.
Once you provide the next line (assuming its not empty/all whitespace), it will get a non-whitespace character and scanf will return.