C++ double pointer array to float conversion

What is a correct way to convert double to float in c++. Is the conversion implicit?

Question 1: Consider double d = 5.0; and float f;

Which one is correct?

• f = d;
• f = (float)d;
• f = static_cast<float>(d);

Question 2: Now consider we have

char *buffer = readAllBuffer(); 
double *d = (const double*)(buffer + offset);
float f;

Which one is now correct?

• f = d[0];
• f = (float)d[0];
• f = static_cast<float>(d[0]);

Thanks in advance!