View Compilation Error

0_0_18658777_19103.cpp:21:16: error: 'M' was not declared in this scope
     char color[M];  
                ^
0_0_18658777_19103.cpp:23:4: error: 'M' was not declared in this scope
 }s[M];  
    ^
0_0_18658777_19103.cpp: In function 'int main()':
0_0_18658777_19103.cpp:36:26: error: 's' was not declared in this scope
             scanf("%s%d",s[i].color,&s[i].number);  
                          ^
0_0_18658777_19103.cpp:37:14: error: 's' was not declared in this scope
         sort(s,s+n,cmp);  
              ^