cclplus: warning: command line option '-std=c11' is valid for C/Objc but not for c++ [enabled by default] /tmp/ccXQ1BgT.o: In function 'main': challenge6.25.cpp: (.text+0xb4) : undefined reference to 'passedSeconds(int, int, int)' collect2: error: ld returned 1 exit status /tmp/ccXMcf75.0: In function main': challenge6.25.cpp: (.text+0xb4) : undefined reference to 'passedSeconds(int, int, int)' collect2: error: ld returned 1 exit status.