DOKK / manpages / debian 11 / tcl8.6-doc / incr.3tcl.en
incr(3tcl) Tcl Built-In Commands incr(3tcl) 







incr - Increment the value of a variable








incr varName ?increment?










Increments the value stored in the variable whose name is
    varName. The value of the variable must be an integer. If
    increment is supplied then its value (which must be an integer) is
    added to the value of variable varName; otherwise 1 is added to
    varName. The new value is stored as a decimal string in variable
    varName and also returned as result.


Starting with the Tcl 8.5 release, the variable varName
    passed to incr may be unset, and in that case, it will be set to the
    value increment or to the default increment value of 1.








Add one to the contents of the variable x:






incr x




Add 42 to the contents of the variable x:






incr x 42




Add the contents of the variable y to the contents of the
    variable x:






incr x $y




Add nothing at all to the variable x (often useful for
    checking whether an argument to a procedure is actually integral and
    generating an error if it is not):






incr x 0










expr(3tcl), set(3tcl)








add, increment, variable, value







  

    
    Tcl