Language: C

n[7]={"Sun","Mon","Tues","Wednes","Thurs","Fri","Satur"};m;main(d){for(;scanf("%d%d",&m,&d)*m;printf("%sday\n",n[(3+(m<3?0:2)+((m+9)%12*13+47)/5+d)%7]));}

Compiler output:
main.c:1:1: warning: data definition has no type or storage class
    1 | n[7]={"Sun","Mon","Tues","Wednes","Thurs","Fri","Satur"};m;main(d){for(;scanf("%d%d",&m,&d)*m;printf("%sday\n",n[(3+(m<3?0:2)+((m+9)%12*13+47)/5+d)%7]));}
      | ^
main.c:1:1: error: type defaults to 'int' in declaration of 'n' [-Wimplicit-int]
main.c:1:13: error: excess elements in 'int[7]' initializer
    1 | n[7]={"Sun","Mon","Tues","Wednes","Thurs","Fri","Satur"};m;main(d){for(;scanf("%d%d",&m,&d)*m;printf("%sday\n",n[(3+(m<3?0:2)+((m+9)%12*13+47)/5+d)%7]));}
      |             ^~~~~
main.c:1:13: note: (near initialization for 'n')
main.c:1:19: error: excess elements in 'int[7]' initializer
    1 | n[7]={"Sun","Mon","Tues","Wednes","Thurs","Fri","Satur"};m;main(d){for(;scanf("%d%d",&m,&d)*m;printf("%sday\n",n[(3+(m<3?0:2)+((m+9)%12*13+47)/5+d)%7]));}
      |                   ^~~~~~
main.c:1:19: note: (near initialization for 'n')
main.c:1:26: error: excess elements in 'int[7]' initializer
    1 | n[7]={"Sun","Mon","Tues","Wednes","Thurs","Fri","Satur"};m;main(d){for(;scanf("%d%d",&m,&d)*m;printf("%sday\n",n[(3+(m<3?0:2)+((m+9)%12*13+47)/5+d)%7]));}
      |                          ^~~~~~~~
main.c:1:26: note: (near initialization for 'n')
main.c:1:35: error: excess elements in 'int[7]' initializer
    1 | n[7]={"Sun","Mon","Tues","Wednes","Thurs","Fri","Satur"};m;main(d){for(;scanf("%d%d",&m,&d)*m;printf("%sday\n",n[(3+(m<3?0:2)+((m+9)%12*13+47)/5+d)%7]));}
      |                                   ^~~~~~~
main.c:1:35: note: (near initialization for 'n')
main.c:1:43: error: excess elements in 'int[7]' initializer
    1 | n[7]={"Sun","Mon","Tues","Wednes","Thurs","Fri","Satur"};m;main(d){for(;scanf("%d%d",&m,&d)*m;printf("%sday\n",n[(3+(m<3?0:2)+((m+9)%12*13+47)/5+d)%7]));}
      |                                           ^~~~~
main.c:1:43: note: (near initialization for 'n')
main.c:1:49: error: excess elements in 'int[7]' initializer
    1 | n[7]={"Sun","Mon","Tues","Wednes","Thurs","Fri","Satur"};m;main(d){for(;scanf("%d%d",&m,&d)*m;printf("%sday\n",n[(3+(m<3?0:2)+((m+9)%12*13+47)/5+d)%7]));}
      |                                                 ^~~~~~~
main.c:1:49: note: (near initialization for 'n')
main.c:1:6: error: cannot initialize array of 'int' from a string literal with type array of 'char'
    1 | n[7]={"Sun","Mon","Tues","Wednes","Thurs","Fri","Satur"};m;main(d){for(;scanf("%d%d",&m,&d)*m;printf("%sday\n",n[(3+(m<3?0:2)+((m+9)%12*13+47)/5+d)%7]));}
      |      ^
main.c:1:58: warning: data definition has no type or storage class
    1 | n[7]={"Sun","Mon","Tues","Wednes","Thurs","Fri","Satur"};m;main(d){for(;scanf("%d%d",&m,&d)*m;printf("%sday\n",n[(3+(m<3?0:2)+((m+9)%12*13+47)/5+d)%7]));}
      |                                                          ^
main.c:1:58: error: type defaults to 'int' in declaration of 'm' [-Wimplicit-int]
main.c:1:60: error: return type defaults to 'int' [-Wimplicit-int]
    1 | n[7]={"Sun","Mon","Tues","Wednes","Thurs","Fri","Satur"};m;main(d){for(;scanf("%d%d",&m,&d)*m;printf("%sday\n",n[(3+(m<3?0:2)+((m+9)%12*13+47)/5+d)%7]));}
      |                                                            ^~~~
main.c: In function 'main':
main.c:1:60: error: type of 'd' defaults to 'int' [-Wimplicit-int]
main.c:1:73: error: implicit declaration of function 'scanf' [-Wimplicit-function-declaration]
    1 | n[7]={"Sun","Mon","Tues","Wednes","Thurs","Fri","Satur"};m;main(d){for(;scanf("%d%d",&m,&d)*m;printf("%sday\n",n[(3+(m<3?0:2)+((m+9)%12*13+47)/5+d)%7]));}
      |                                                                         ^~~~~
main.c:1:1: note: include '<stdio.h>' or provide a declaration of 'scanf'
  +++ |+#include <stdio.h>
    1 | n[7]={"Sun","Mon","Tues","Wednes","Thurs","Fri","Satur"};m;main(d){for(;scanf("%d%d",&m,&d)*m;printf("%sday\n",n[(3+(m<3?0:2)+((m+9)%12*13+47)/5+d)%7]));}
main.c:1:73: warning: incompatible implicit declaration of built-in function 'scanf' [-Wbuiltin-declaration-mismatch]
    1 | n[7]={"Sun","Mon","Tues","Wednes","Thurs","Fri","Satur"};m;main(d){for(;scanf("%d%d",&m,&d)*m;printf("%sday\n",n[(3+(m<3?0:2)+((m+9)%12*13+47)/5+d)%7]));}
      |                                                                         ^~~~~
main.c:1:73: note: include '<stdio.h>' or provide a declaration of 'scanf'
main.c:1:95: error: implicit declaration of function 'printf' [-Wimplicit-function-declaration]
    1 | n[7]={"Sun","Mon","Tues","Wednes","Thurs","Fri","Satur"};m;main(d){for(;scanf("%d%d",&m,&d)*m;printf("%sday\n",n[(3+(m<3?0:2)+((m+9)%12*13+47)/5+d)%7]));}
      |                                                                                               ^~~~~~
main.c:1:95: note: include '<stdio.h>' or provide a declaration of 'printf'
main.c:1:95: warning: incompatible implicit declaration of built-in function 'printf' [-Wbuiltin-declaration-mismatch]
main.c:1:95: note: include '<stdio.h>' or provide a declaration of 'printf'