int main() { add(); minus(); mutilplication(); divide(); return 0; }
void choose() { int n; scanf("%d",&n); getchar(); // system(cls); switch(n) { case 1:add(); break; case 2:minus();break; case 3:mutilplication();break; case 4:divide();break; case 5:matrix_UI(); break; //////////////////////////// case 6:opera(); } }