/in/foo.c: In function 'main':
/in/foo.c:14:9: warning: implicit declaration of function 'fabs' [-Wimplicit-function-declaration]
    b[j]=fabs(a[j]-a[k])+b[j];
         ^~~~
/in/foo.c:14:9: warning: incompatible implicit declaration of built-in function 'fabs'
/in/foo.c:14:9: note: include '<math.h>' or provide a declaration of 'fabs'