foo.c:3:1: error: unknown type name 'using'
foo.c:3:17: error: expected '=', ',', ';', 'asm' or '__attribute__' before 'std'
foo.c:9:15: error: expected ';', ',' or ')' before '&' token
foo.c: In function 'add':
foo.c:21:5: warning: implicit declaration of function 'swap' [-Wimplicit-function-declaration]
foo.c:20:9: warning: unused variable 'z' [-Wunused-variable]
foo.c: In function 'main':
foo.c:60:2: warning: unknown conversion type character 'l' in format [-Wformat]
foo.c:60:2: warning: too many arguments for format [-Wformat-extra-args]