Used to reverse the result of any expression. Here in the output, you can see the value of 'a' has now become 1 from 0. While the value of 'b' has become 0 from 1. If condition-exp is true, exp1 is evaluated and the result is returned. If the cond-exp is false, exp2 is evaluated and its result is returned.
In our example, exp1 is true as the value of A is greater than 6. String comparison operator compares the value of both operands. If the value of operand are same, then it will return 1 else return 0. In example value for both A and B is 7, therefore result return 1.
If the required value found in the defined list, it returns 1 else return 0. In example value 1 exists in variable 'a' hence it will return 1. There are various flow control and decision making command which are used to alter the flow of a program. Program executions always start from the top of source file to the bottom. The switch statement enables a variable to be tested for equality against a list of values. It evaluates the list of values and returns the result of that evaluation.
If no values matches then default values will be returned. Example : In the following example, value of a is , and with the same code we switch statement for another value of b is The out will show value for both a and b. Loop statement allows executing a statement or group of statement multiple times. Tcl provides the following types of looping statement. When a given condition is true then a statement or group of statement repeats which are in the loop body.
In the above example, "incr" built-in command is used. It executes a sequence of statements multiple times based upon a counter value. A Tcl script consists of one or more commands, separated by newlines or semicolons. Evaluating a command Two step process: parsing and execution.
Parsing: Tcl does not apply any meaning to the value of the words. It only performs simple string operations, e. Tcl only makes one pass for substitutions each character is scanned exactly once.
The result of one substitution is not scanned for further substitutions. Execution: meaning is applied to the arguments of the command. Tcl checks to see if the command is defined, assumed to be the first word in the sequence of words, and locates a command procedure to execute.
Variable,command and backslash substitutions State is maintained in Tcl through the use of variables, and are both declared and instantiated with the "set" command. Variable substitution can occur anywhere in a word e. Braces defer evaluation. To see the output immediately after the command runs, we can use the flush command. The stdout is the standard output.
In our case it is a terminal; it is called a channel id in Tcl. The gets command reads a line from the standard input. The result is stored in the name variable. If a parameter is passed to the command, then its value is added to the value of the variable; otherwise the value is incremented by 1.
Number 4 is added to the x variable. The puts command prints 10 to the console. The set command is used to create and read variables. The unset command destroys a variable. This line also prints the value of the x variable.
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