Compilare: user.c: In function ‘dif’: user.c:24:2: warning: implicit declaration of function ‘abs’ [-Wimplicit-function-declaration] return abs(a - b); ^ user.c: In function ‘main’: user.c:32:8: warning: ignoring return value of ‘fscanf’, declared with attribute warn_unused_result [-Wunused-result] fscanf(file,"%d %d",&a,&b); ^