call of overloaded function is ambiguous, double vs float

Question

Whenever I run this code...

#include <iostream>

int add(int x, int y){
    return x+y;
} 

float add(float x, float y){
    return x+y;
}

int main(){
    using namespace std;
    add(1.11, 1.11);
    return 0;
}

... I get this error:

18.cpp: In function ‘int main()’:
18.cpp:24:16: error: call of overloaded ‘add(double, double)’ is ambiguous
  add(1.11, 1.11);
                ^
18.cpp:24:16: note: candidates are:
18.cpp:7:5: note: int add(int, int)
 int add(int x, int y){
     ^
18.cpp:11:7: note: float add(float, float)
 float add(float x, float y){

I thought 1.11 would be clearly a float, not an integer. When I change float to double, the program works.

Why does C++ say the call is ambiguous?

Answer 1

In C++ the type of decimal literals like 1.11 is defined to be double. Given that it has to convert the double to either int or float which results in the ambiguity.

A literal with an f suffix like 1.11f would have type float.