Compilare: user.c: In function ‘back’: user.c:30:13: warning: unused variable ‘i’ [-Wunused-variable] int i; ^ user.c:59:1: warning: control reaches end of non-void function [-Wreturn-type] } ^ user.c: In function ‘main’: user.c:66:11: warning: ignoring return value of ‘fscanf’, declared with attribute warn_unused_result [-Wunused-result] fscanf(f,"%d%d",&n,&m); ^ user.c:70:19: warning: ignoring return value of ‘fscanf’, declared with attribute warn_unused_result [-Wunused-result] fscanf(f,"%ld",&a[i][j]); ^