Replaces a portion of a string with another string.
MID$(string_variable,start_offset[ ,num_char])=string_expression
string_variable is the string variable to be modified.
start_offset is the position of the first character to be replaced in the string variable.
num_char is the number of characters in the string to replace. If you omit this value, MID$ uses the length of the replacement string.
string_expression is any string expression.
a$ = "ABCDEF"
MID$(a$, 2, 2) = "bc"
PRINT a$
ABcDEF