foo.cc:10:7: warning: character constant too long for its type
    if('90~100')
       ^~~~~~~~
foo.cc:14:12: warning: character constant too long for its type
    else if('80~89')
            ^~~~~~~
foo.cc:18:12: warning: character constant too long for its type
    else if('70~79')
            ^~~~~~~
foo.cc:22:12: warning: character constant too long for its type
    else if('60~69')
            ^~~~~~~
foo.cc:27:12: warning: multi-character character constant [-Wmultichar]
    else if('0~59')
            ^~~~~~

[Hydro](https://hydro.ac)提供评测服务