[Error] Character range read by %c

When I was writing a question recently, the data length is
nowcoder
6
A 1
M 4
A 6
M -3
M 1
A 1
I used scanf("%c %lld",&op,&x) to read the error, and I
feel it should be% c reading problem, use %s to read an array, the problem is solved

Record it