Compilare: user.c: In function ‘main’: user.c:30:1: warning: passing argument 1 of ‘toupper’ makes integer from pointer without a cast [enabled by default] toupper(letters); toupper(expression); ^ In file included from /usr/include/features.h:357:0, from /usr/include/stdio.h:28, from user.c:1: /usr/include/ctype.h:223:1: note: expected ‘int’ but argument is of type ‘char *’ __NTH (toupper (int __c)) ^ user.c:30:1: warning: passing argument 1 of ‘toupper’ makes integer from pointer without a cast [enabled by default] toupper(letters); toupper(expression); ^ In file included from /usr/include/features.h:357:0, from /usr/include/stdio.h:28, from user.c:1: /usr/include/ctype.h:223:1: note: expected ‘int’ but argument is of type ‘char *’ __NTH (toupper (int __c)) ^ user.c:44:22: 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", &nChanges); ^ user.c:28:7: warning: ignoring return value of ‘fscanf’, declared with attribute warn_unused_result [-Wunused-result] fscanf(file1, "%s", letters); ^