Is a += b more efficient than a = a + b in C?

Question

I know in some languages the following:

a += b

is more efficient than:

a = a + b

because it removes the n

Answer 1

This is a compiler specific question really, but I expect all modern compilers would give the same result. Using Visual Studio 2008:

int main() {  
    int a = 10;  
    int b = 30;  
    a = a + b;  
    int c = 10;  
    int d = 50;  
    c += d;  
}  

The line a = a + b has disassembly

0014139C  mov         eax,dword ptr [a]   
0014139F  add         eax,dword ptr [b]   
001413A2  mov         dword ptr [a],eax   

The line c += d has disassembly

001413B3  mov         eax,dword ptr [c]   
001413B6  add         eax,dword ptr [d]   
001413B9  mov         dword ptr [c],eax   

Which is the same. They are compiled into the same code.