foo.cc: In function 'void make(char (*)[101], int, int)':
foo.cc:75:24: error: 'arc4random' was not declared in this scope
             a[i][j] = (arc4random() % 100) > 20 ? '-' : '#';
                        ^~~~~~~~~~
foo.cc:75:24: note: suggested alternative: 'srandom'
             a[i][j] = (arc4random() % 100) > 20 ? '-' : '#';
                        ^~~~~~~~~~
                        srandom

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