Compilare: user.c: In function ‘main’: user.c:16:1: warning: implicit declaration of function ‘strlen’ [-Wimplicit-function-declaration] len = strlen(number); ^ user.c:16:7: warning: incompatible implicit declaration of built-in function ‘strlen’ [enabled by default] len = strlen(number); ^ user.c:18:5: warning: implicit declaration of function ‘isdigit’ [-Wimplicit-function-declaration] if(isdigit(number[i])){ ^ user.c:5:23: warning: variable ‘file3’ set but not used [-Wunused-but-set-variable] FILE *file1, *file2, *file3; ^ user.c:13:7: warning: ignoring return value of ‘fscanf’, declared with attribute warn_unused_result [-Wunused-result] fscanf(file1, "%lld %lld", &B, &K); ^ user.c:14:7: warning: ignoring return value of ‘fscanf’, declared with attribute warn_unused_result [-Wunused-result] fscanf(file1, "%s", number); ^