View Compilation Error

0_0_22924025_11800.cpp: In function 'int main()':
0_0_22924025_11800.cpp:10:21: error: 'swap' was not declared in this scope
             swap(a,b);
                     ^
0_0_22924025_11800.cpp:13:21: error: 'swap' was not declared in this scope
             swap(a,c);
                     ^
0_0_22924025_11800.cpp:16:21: error: 'swap' was not declared in this scope
             swap(b,c);
                     ^