Control Structures
Sequence control statements
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This type of statements insured that
the instruction in a program is executed in the same order. In which they
appear in the program.
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Decision control & conditional
statements
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Decision control statements and Conditional Statements
allow the computer to take decision. And force to work under given condition:
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Decision control statements:
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It gives the control to the computer
for taking the decisions.
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Two decisions control instruction
which are implemented in C are following:
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a) The if statements.
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b) The if-else statements.
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General form of if statements
is:
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if (condition is true) execute this statement;
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Here we can add else statement also
as follow:
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else
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printf("you have enter number
greater than 50");
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}
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Case control statements
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The Case control statements
allow the computer to take decision as to be which statements are to be
executed next. It is a multi way decision construct facilitate number of
alternatives.
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C has multi way decision statement
known as switch statements. It tests the value of a given variable or
expression against a list of case value and when a match found a block of
statement associated with the case is executed.
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Syntax of switch statement:
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switch(expression)
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{
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case constant_1:
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statements;
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case constant_2:
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statements;
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case constant_n:
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statements;
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default:
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statements;
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}
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Explanation:
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First in expression parentheses we
give the condition.
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This condition checks to match, one
by one with case constant.
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If value match then its statement
will be executed. Otherwise the default statement will appear.
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Repitition & loop control
statements
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This type of statements helps the
computer to execute a group of statements repeatedly.
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This allows a set of instruction to
be performed until a certain condition is reached.
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There are three types of loops in C:
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1. for loop
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2. while loop
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3. do-while loop
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The for loop
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There are three parts of for
loop:
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a)counter initialization.
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b)check condition
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c)modification of counter.
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Syntax:
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for (variable initialize; check condition;
modify counter)
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{
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statements 1;
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-----------;
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-----------;
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statements n;
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}
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Explanation:
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1. The initialization is usually an
assignment that is used to set the loop control variable.
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2. The condition is a relational
expression that determines when the loop will exit.
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3. The modify counter defines
how loop control variables will change each time the loop is
repeated.
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These three sections are separated
by semicolon (;).
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The for loop is
executed as long as the condition is true. When, the condition becomes false
the programe execution will resume on the statement following the block.
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Advantage of for loop over
other loops:
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All three parts of for loop (i.e.
counter initialization, check condition, modification of counter) are
implemented on a single line.
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Something more about for loop:
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1. for
(p=1,n=2;n<17 b="" n=""> we can assign multiple variable together
in for loop.
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2. for
(n=1,m=50;n<=m;n=n+1,m=m-1):-The increment section may also have more
than one part as given.
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3. for
(i=1,sum=0;i<20 amp="" b="" i="" sum="">The test condition may have
any compound relation as given.
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4. for
(x=(m+n)/2;x>0;x=x/2):-It is also permissible to use expressions in
the assignment statements of initialization and increment section as given.
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5. for (;m!=100;):-we can
omitted the initialization and increment section to set up time delay.
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while loop
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It is a primitive type looping
control because it repeats the loop a fixed no. of time. It
is also called entry controlled loop statements.
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Syntax:
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while (test_condition)
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{
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body of loop
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}
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Explanation:
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The test condition is evaluated if
the condition is true, the body of loop will be executed.
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The do-while loop
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The minor Difference between the
working of while and do-while loop is the
place where the condition is tested.
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The while tests the condition before
executing any of the statements within the while loop
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As against this, the do-while
loop tests the condition after having executed the statement within
the loop.
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syntax:
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do
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{
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body of loop;
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}
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while (test condition);
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Some more statements
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The break Statement
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We have already met break in the
discussion of the switch statement. It is used to exit from a loopor
a switch, passing control to the first statement beyond the loop or
a switch.
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With loops, break can be
used to force an early exit from the loop, or to implement a loop with
a test to exit in the middle of the loop body.
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A break within a loop should
always be protected within an if statement which provides the test to control
the exit condition.
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The continue Statement
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This is similar to break but is
encountered less frequently. It only works within loops where its
effect is to force an immediate jump to the loop control
statement.
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In a while loop, jump
to the test statement.
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In a do while loop, jump
to the test statement.
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In a for loop, jump to
the test, and perform the iteration (looping).
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Like a break, continue should be
protected by an if statement. You are unlikely to use it very often.
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The goto Statement
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C has a goto statement which permits
unstructured jumps to be made. It requires a label in order to identify the
place where the branch is to be made.
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A label is any valid variable name,and
must be followed by a colon(:).
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Syntax:
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goto label;
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..................
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label:
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statement;
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The label can be any where in the
program either before or after the goto label; statement.
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The exit() function
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This function is used for terminating
the execution of C program.
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Syntax:
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exit(int status);
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