Compilare: user.c: In function ‘main’: user.c:20:1: warning: implicit declaration of function ‘isalpha’ [-Wimplicit-function-declaration] while(isalpha(ch = fgetc(file1))){ ^ user.c:10:33: warning: unused variable ‘b’ [-Wunused-variable] int i, j, N, swaps = 0, a = -1, b = -1, c = -1; ^ user.c:10:25: warning: unused variable ‘a’ [-Wunused-variable] int i, j, N, swaps = 0, a = -1, b = -1, c = -1; ^ user.c:17:7: warning: ignoring return value of ‘fscanf’, declared with attribute warn_unused_result [-Wunused-result] fscanf(file1, "%d", &N); ^