This is the code for finding the maximum of four numbers:

```cpp
#include <iostream>
#include <cstdio>
using namespace std;

int max_of_four(int a,int b,int c,int d) {
    if(a>b&&a>c&&a>d)
    return a;
    else if(b>a&&b>c&&b>d)
    return b;
    else if(c>a&&c>b&&c>d)
    return c;
    else if(d>a&&d>c&&d>b)
    return d;
}

int main() {
  int a,b,c,d;
  scanf("%d %d %d %d",&a,&b,&c,&d);
  int ans;
  ans=max_of_four(a,b,c,d);
  printf("%d",ans);
  return 0;
}

```

But I am getting a warning like this:

> 
> control reaches end of non-void function -wreturn-type
> 
> 
> 

What does this error mean?  

Why does this error occur?