Compilare: user.c: In function ‘main’: user.c:42:22: warning: operation on ‘j’ may be undefined [-Wsequence-point] boolVar[letters[j++] - 'A'] = 1 - boolVar[letters[j] - 'A']; ^ user.c:14:16: warning: unused variable ‘k’ [-Wunused-variable] int i=-1, j=0, k=0, nChanges; ^ user.c:27:7: warning: ignoring return value of ‘fscanf’, declared with attribute warn_unused_result [-Wunused-result] fscanf(file1, "%d\n", &nChanges); ^ user.c:28:7: warning: ignoring return value of ‘fscanf’, declared with attribute warn_unused_result [-Wunused-result] fscanf(file1, "%s\n", letters); ^