Control Statements
Control
statements are used to transfer the control form one place of the program to
other place. Generally we use 3 types of operators when working with control
statements. They are
1. Relational
operators (< , > , < =, > =)
2. Equality
operators (= =, ! =).
3. Logical
operators (&&,││ , !)
‘C’ language provides 3 types of control statements. They
are
1. Conditional
statements
2. Unconditional
statements.
3. Iterative
statements.
Conditional
statements
These are used to execute a group
of statements based on a condition.
Simple- if:
This statement is used
to execute group of statements if the condition is true. Otherwise they are not
executed. The syntax of simple if as follows.
if(condition)
{
Statement-1;
Statement-2;.
………..
Statement n;
}
Next statement.
Example:
If-else:
It is used to execute a group of statements
if the condition is true otherwise the statements which are related to false
block are executed.
Syntax: if(condition)
{
Statements
related to true;
}
else
{
Statements
related to false;
}
Nested if…else:
Nested if contains if
else statements under and if and another else statements.
|
{
if(condition)
{
Statements;
}
else
{
Statements;
}
}
else
{
Statements;
}
Flow Chart
if…else…if (Ladder if):
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Example:
Switch statement
The switch statement
allows us to select from multiple choices based on a set of fixed values for a
given expression.
The common switch statement syntax:
switch(expression)
{
case value1:
/* execute unit of code 1 */
break;
case value2:
/* execute unit of code 2 */
break;
...
default: /*
execute default action */
break;
}
·
In the switch statement, the
selection is determined by the value of an expression that you specify which is
enclosed between the parentheses after the keyword switch.
·
The case constant expression must be an integer
value and all values in case statement are equal.
·
When a break statement is executed, it
causes execution to continue with the statement following the closing brace for
the switch.
·
The break statement is not mandatory,
but if we don't put a break statement at the end of the statements for
a case, the statements for the next case in sequence will be executed as well,
through to whenever another break is found or the end of the switch block is
reached. This can lead some unexpected program logics happen.
·
The default statement is the default
choice of the switch statement if all cases statement are not satisfy with the expression.
·
The break
after the default statements is not necessary unless you put another case
statement below it.
Here is an example of using C switch statement
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Looping control
statements
To execute a set of instructions
repeatedly until a particular condition is being satisfied.
Three types of looping statements
are there
1)
While Loop
2) Do
while Loop
3)
For Loop
While Loop Statement
A loop statement allows you to execute a
statement or block of statements repeatedly. The while loop is used
when you want to execute a block of statements repeatedly with checked
condition before making an iteration.
Syntax of while
loop statement:
while (expression)
{
// statements
}
This loop executes as long as the given logical
expression between parentheses after while is true. When expression is
false, execution continues with the statement following the loop block. The expression is checked at the beginning of the loop, so if
it is initially false, the loop statement block will not be executed at all.
And it is necessary to update loop conditions in loop body to avoid loop
forever. If you want to escape loop body when certain conditions meet, you can
use break statement
Here is a while loop statement demonstration
program:#include <stdio.h>
main( )
{
int x = 10;
int i = 0;
// using while loop statement
while(i < x)
{
i++;
printf("%d\n",i);
}
// when number 5 found, escape loop body
int numberFound= 5;
int j = 1;
while(j < x)
{
if(j == numberFound)
{
printf("number found\n");
break;
}
printf("%d...keep finding\n",j);
j++;
}
}
Do-while Loop Statement
do while loop statement allows us
to execute code block in loop body at least one.
Here is do while loop syntax:
do
{
// statements
}
while (expression);
Example:
#include <stdio.h>
Output:1 2 3 4 5
main()
{
int x = 5;
int i = 0;
// using do while loop statement
do{
i++;
printf("%d\n",i);
} while(i < x);
}
The program above print exactly 5 times as indicated in do
while loop body
For Loop Statement
Syntax:
for (initialization_expression; loop_condition; increment_expression)
{
// statements
}
There
are three parts which is separated by semi-colons in control block of the for
loop.
- initialization_expression is executed before execution of the loop starts. This is typically used to initialize a counter for the number of loop iterations. You can initialize a counter for the loop in this part.
- The execution of the loop continues until the loop_condition is false. This expression is checked at the beginning of each loop iteration.
- The increment_expression, is usually used to increment the loop counter. This is executed at the end of each loop iteration.
/* check whether a number is prime or not */
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#include <stdio.h>
main()
{
// using for loop statement
int max = 5;
int i = 0;
for(i = 0; i < max;i++)
{
printf("%d\n",i);
}
}
