Main.cc: In function 'int main()': Main.cc:6:17: error: 'abs' was not declared in this scope if(abs(n+m>b)&&(n-m>b)){ ^ Main.cc:5:29: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result] scanf("%d%d%d",&n,&m,&b); ^