foo.cpp: In function 'void mul(num&, const num&, int)':
foo.cpp:23:4: error: incompatible types in assignment of 'int' to 'char [1000]'
 c.n+=m%r;
    ^
foo.cpp:25:9: error: ISO C++ forbids comparison between pointer and integer [-fpermissive]
 if(c.n>=r) c.n-=r,m++;
         ^
foo.cpp:25:15: error: incompatible types in assignment of 'int' to 'char [1000]'
 if(c.n>=r) c.n-=r,m++;
               ^
foo.cpp:27:10: error: incompatible types in assignment of 'int' to 'char [1000]'
 if(m) c.n=m;
          ^