brainfuck, 145 bytes
+++++++++[>++++++++++<-]>+[>+>+<<-]>>++>,>+++++++++[<----->-]<--->>>,>+++++++++[<----->-]<--->++++++++++<[<<<[>+>+<<-]>[<<<.>.>>-]>[<<+>>-]>>.<-]
Pruébalo en línea!
¡Mi primer código de golf! ¡Hurra!
La entrada está en ascii + 48, por lo que para hacer 50, 50 debe ingresar b, b (las letras ascii para 98)
Explicación
+++++++++[>++++++++++<-]>+ Get the opening square bracket into first position
[>+>+<<-] Get it into the second and third position
>>++ Get the third position to be the closing bracket
>
,>+++++++++[<----->-]<--- Get first number into fourth cell
>>>
,>+++++++++[<----->-]<--- Get second number into seventh cell
>++++++++++ get newline into 8th position
<
[ Start our height loop
<<<[>+>+<<-] Get the width into the fifth and sixth positions
>[ Start our width loop at the fifth position
<<<.>. Print the second and third positions
>>-] Decrement the fifth position
>
[<<+>>-] copy the sixth position into the fourth position
>>. print newline
<-]