whitespace in the format string (scanf)

Question

Consider the following code:

#include<stdio.h>
int main() {
    int i=3, j=4;
    scanf("%d c %d",&i,&j);
    printf("%d %d",i,j);
    return 0;
}

It works if I give 2c3 or 2 c 3 or 2c 3 as input if I have to change the value of variables. What should I do if I want the user to enter the same pattern as I want means if %dc%d then only 2c3 is acceptable and not 2 c 3 and vice versa if it is %d c %d?

Answer 1

Whitespace in the format string matches 0 or more whitespace characters in the input.

So "%d c %d" expects number, then any amount of whitespace characters, then character c, then any amount of whitespace characters and another number at the end.

"%dc%d" expects number, c, number.

---

Also note, that if you use * in the format string, it suppresses assignment:
%*c = read 1 character, but don't assign it to any variable

So you can use "%d%*c c%*c %d" if you want to force user to enter: number, at least 1 character followed by any amount of whitespace characters, c, at least 1 character followed by any amount of whitespace characters again and number.