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Conditional Flow Control
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Conditional flow like in any other programming language is used for controlling execution a block of code, when a condition is true.
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if then else
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if then else is used for checking for a condition and if condition is true, then the block of code inside the {} is excuted.
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Syntax:
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if bool-exp [then] {action; ...} [else if bool-exp [then] {action; ...}] [else {action; ...}]
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Syntax : if
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if (condition) {
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statements;
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};
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Syntax : if-else
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if (condition) {
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statements;
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} else {
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statements;
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};
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Syntax : nested if-else-if
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if (condition) {
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statements;
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} else if (condition) {
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statements;
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}
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................
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................
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} else {
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statements;
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};
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if then else clause comprises one action, the semicolon comes at the end of the clause and not after each action block within the clause.
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Example - if then else
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1 <'
2 extend sys {
3 run() is also {
4 var a : int = 10;
5 var b : int = 11;
6 var c : int = 12;
7 outf("a = %d b = %d\n",a,b);
8 if a > b {
9 out("a is greater then b");
10 } else {
11 out("a is less then b");
12 };
13 if (a > b) then { // then is optional
14 out("a is greater then b");
15 } else if (b > c) then {
16 out("b is greater then c");
17 } else if (c > a) then {
18 out("c is greater then a");
19 };
20 };
21 };
22 '>
You could download file flow_control1.e
here
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Simulator Output
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a = 10 b = 11
a is less then b
c is greater then a
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case labeled-case-item
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Execute an action block based on whether a given comparison is true. Evaluates the case-exp and executes the first action-block for which label-case-item matches the case-exp. If no label--case-item equals the case-exp, executes the default-action block, if specified.
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Syntax
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case case-exp {labeled-case-item; ... [default: {default-action; ...}]}
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Example - case labeled-case-item
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1 <'
2 struct packet {
3 length: int;
4 keep length < 513;
5 keep length > 63;
6 };
7
8 struct tx_gen {
9 ! packet: packet;
10
11 txgen () is {
12 var i : int = 4;
13 for i from 0 to 4 do {
14 gen packet;
15 packet_class();
16 };
17 };
18
19 packet_class () is {
20 outf("Current size of packet : %d ",packet.length);
21 case packet.length {
22 64: {
23 out("minimal packet");
24 };
25 [65..256]: {
26 out("short packet");
27 };
28 [256..512]: {
29 out("long packet");
30 };
31 default: {
32 out("illegal packet length");
33 };
34 };
35 };
36 };
37
38 extend sys {
39 U_txgen : tx_gen;
40 run() is also {
41 U_txgen.txgen();
42 };
43 };
44 '>
You could download file flow_control2.e
here
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Simulator Output
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Current size of packet : 175 short packet
Current size of packet : 479 long packet
Current size of packet : 78 short packet
Current size of packet : 438 long packet
Current size of packet : 158 short packet
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case bool-case-item
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Evaluates the bool-exp conditions one after the other; executes the action-block associated with the first TRUE bool-exp. If no bool-exp is TRUE, executes the default-action-block, if specified. Each of the bool-exp conditions is independent of the other bool-exp conditions, and there is no main case-exp to which all cases refer. This case action has the same functionality as a single if then else action in which you enter each bool-case-item as a separate else if then clause.
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Syntax
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case {bool-case-item; ... [default {default-action; ...}]}
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Example - case bool-case-item
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1 <'
2 struct packet {
3 length: int;
4 keep length < 513;
5 keep length > 63;
6 };
7
8 struct tx_gen {
9 ! packet: packet;
10
11 txgen () is {
12 var i : int = 4;
13 for i from 0 to 4 do {
14 gen packet;
15 packet_class();
16 };
17 };
18
19 packet_class () is {
20 outf("Current size of packet : %d ",packet.length);
21 case {
22 (packet.length == 64) {
23 out("minimal packet");
24 };
25 (packet.length >= 65 && packet.length <=256) {
26 out("short packet");
27 };
28 (packet.length >=256 && packet.length <= 512) {
29 out("long packet");
30 };
31 default {
32 out("illegal packet length");
33 };
34 };
35 };
36 };
37
38 extend sys {
39 U_txgen : tx_gen;
40 run() is also {
41 U_txgen.txgen();
42 };
43 };
44 '>
You could download file flow_control3.e
here
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Simulator Output
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Current size of packet : 175 short packet
Current size of packet : 479 long packet
Current size of packet : 78 short packet
Current size of packet : 438 long packet
Current size of packet : 158 short packet
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