Character Array User Input Scanf - c

Question

Just started learning programming on my own and whilst trying to create an array of characters from user input, using scanf, have hit the wall; the code is as below:
#include <stdio.h>
#define I 5
int main (void) {
char a[I+1] = {a[I+1] = '\0'}, q;
int i;
for(i = 0; i < I; i++) {
printf("Enter an alphabet:\t");
//scanf("%c", &q);
//scanf("%c*\n", &q);
//scanf("%[^\n]", &q);
//scanf("%[a-z, A-Z]", &q);
scanf("%127[^\n]", &q);
a[i] = q;
}
printf("\n");
for(i = 0; i < I; i++) {
printf("Element a[%d] of a[I]:\t%c\n", i, a[i]);
}
printf("And the a[I] string:\t%s\n", a);
return 0;
}
None of the scanf combinations in the above code works: the program either skips input prompt after the first one or does not store response.
How can this be resolved with scanf?

Answer 1

char a[I+1] = {a[I+1] = '\0'} is not valid. Even if it compiles, it is going out of bounds when assigning the '\0' character. The commonly used convention looks more like this instead:
char a[I+1] = {0};
Or simply:
char a[I+1] = {};
That said, q is only 1 char in size, but your scanf() is trying to read a string up to 127 chars into q. So you are going to trash memory. To read a single char at a time, use %c instead:
#include <stdio.h>
#include <string.h>
#define MAX_INPUT 5
int main (void) {
char a[MAX_INPUT+1];
int i, len;
for(i = 0; i < MAX_INPUT; i++) {
printf("Enter an alphabet:\t");
scanf("%c", &a[i]);
}
a[MAX_INPUT] = '\0';
printf("\n");
len = strlen(a);
for(i = 0; i < len; i++) {
printf("Element a[%d]:\t%c\n", i, a[i]);
}
printf("And the a string:\t%s\n", a);
return 0;
}
Or, you can remove the loop and just use a single call to scanf() using "%5[^\n]" as the format string:
#include <stdio.h>
#include <string.h>
#define MAX_INPUT 5
int main (void) {
char a[MAX_INPUT+1];
char fmt[20];
int i, len;
sprintf(fmt, "%%%d[^\n]", MAX_INPUT);
printf("Enter an alphabet:\t");
scanf(fmt, a);
printf("\n");
len = strlen(a);
for(i = 0; i < len; i++) {
printf("Element a[%d]:\t%c\n", i, a[i]);
}
printf("And the a string:\t%s\n", a);
return 0;
}

Answer 2

This works without any warning or error on Cygwin gcc v7.3 with Wall flag:
#include <stdio.h>
#define I 5
int main (void) {
char a[I+1] = {a[I+1] = '\0'},q;
int i;
for(i = 0; i < I; i++) {
printf("Enter an alphabet:\t");
scanf("%c%*c", &q);
a[i] = q;
}
printf("\n");
for(i = 0; i < I; i++) {
printf("Element a[%d] of a[I]:\t%c\n", i, a[i]);
}
printf("And the string a[I]:\t%s\n", a);
return 0;
}