View Compilation Error

0_0_35343308_17260.cpp: In function 'void Gauss(double (*)[505], int)':
0_0_35343308_17260.cpp:24:67: error: 'swap' was not declared in this scope
    for ( int j = i ; j <= num + 1 ; j++ ) swap( A[i][j] , A[r][j] ) ;
                                                                   ^