2. Condition
Operator Meaning Example
== Equal to count == 10
!= Not equal to flag != DONE
< Less than a < b
<= Less than or equal to <= LIMIT
> Greater than pointer > end_of_list
>= Greater than or equal to lap >= start
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Guwahati
2
3. Control Structures in C
These include
if else,
while,
do-while,
for, and a selection statement called
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for, and a selection statement called
switch.
4. if-else
The if-else statement can exist in two forms: with or
without the else.The two forms are:
if(expression)
statement
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statement
or
if(expression)
statement1
else
statement2
6. Nested ifNested ifNested ifNested if
if (i == 10) {
if (j < 20) a = b;
if (k > 100) c = d; // this if is
else a = c; // associated with this else
}
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}
else a = d; // this else refers to if(i == 10)
8. ifififif----elseelseelseelse----if Ladderif Ladderif Ladderif Ladder
// Demonstrate if-else-if statements (IfElse.c).
#include <stdio.h>
main () {
int no;
printf(“nEnter any number from 1 to 12 to know the month”);
scanf(“%d”,&no);
Dept. of CS&E and IT, DBCET, Guwahati8
scanf(“%d”,&no);
9. If (no==1)
printf(“n Month is January”);
else if (no==2)
printf(“n Month is February”);
else if (no==3)
printf(“n Month is March”);
else if (no==4)
printf(“n Month is April”);
else if (no==5)
printf(“n Month is May”);
else if (no==6)
printf(“n Month is June”);
else if (no==7)
printf(“n Month is July”);
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printf(“n Month is July”);
else if (no==8)
printf(“n Month is August”);
else if (no==9)
printf(“n Month is September”);
else if (no==10)
printf(“n Month is October”);
else if (no==11)
printf(“n Month is November”);
else if (no==12)
printf(“n Month is December”);
else printf(“ n Invalid Entry”);
}
10. switchswitchswitchswitch
The control statement that allows us to make a decision
from the number of choices is called a switch, or more
correctly a switch-case-default, since these three
keywords go together to make up the control statement.
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keywords go together to make up the control statement.
They most often appear as follows:
11. switchswitchswitchswitch
switch ( integer expression) {
case value1:
// statement sequence
break;
case value2:
// statement sequence
break;
Dept. of CS&E and IT, DBCET, Guwahati11
break;
.
.
.
case valueN:
// statement sequence
break;
default:
// default statement sequence
}
12. switch
The integer expression following the keyword switch is any
C expression that will yield an integer value.
It could be an integer constant like 1, 2 or 3, or an
expression that evaluates to integer.
The keyword case is followed by an integer or a character
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The keyword case is followed by an integer or a character
constant.
Each constant in each case must be different from all the
others.
13. switchswitchswitchswitch
// A simple example of the switch(switch.c)
#include <stdio.h>
main() {
int i;
for(i=0; i<6; i++)
switch(i) {
case 0:
printf("i is zero.n");
break;
case 1:
printf("i is one.n");
break;
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break;
case 2:
printf("i is two.n");
break;
case 3:
printf("i is three.n");
break;
default:
printf("i is greater than 3.n");
} // switch
} // main
14. main()
{
char c = 'x' ;
switch ( c )
{
case 'v' :
printf ( "I am in case v n" ) ;
break ;
case 'a' :
printf ( "I am in case a n" ) ;
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printf ( "I am in case a n" ) ;
break ;
case 'x' :
printf ( "I am in case x n" ) ;
break ;
default :
printf ( "I am in default n" ) ;
}
}
15. Nested switchNested switchNested switchNested switch
switch(count) {
case 1:
switch(target) { // nested switch
case 0:
printf("target is zero");
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printf("target is zero");
break;
case 1: // no conflicts with outer switch
printf("target is one");
break;
} // switch(target)
break;
case 2: // ...
16. switch Versus ifswitch Versus ifswitch Versus ifswitch Versus if----else Ladderelse Ladderelse Ladderelse Ladder
There are some things that we simply cannot do
with a switch. These are:
A float expression cannot be tested using a
switch
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switch
Cases can never have variable expressions (for
example it is wrong to say case a +3 :
Multiple cases cannot use same expressions.
17. Loop structure
The repetitive operation in a program is done through loop-
They are:
(a) Using a for statement
(b) Using a while statement
(c) Using a do-while statement
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(c) Using a do-while statement
18. for loopfor loopfor loopfor loop
for loop allows us to specify the following three things in a
single line-
Setting a loop counter to an initial value.
Testing the loop counter to determine whether its value has
reached the number of iterations desired.
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Increasing the value of loop counter each time the program
segment within the loop has been executed.
General Form:
for(initialization; condition; iteration)
{
// body
}
19. for
// Using the comma (comma.c)
#include <stdio.h>
main() {
int a, b;
for(a=1, b=4; a<b; a++, b--) {
printf("a = %d n", a);
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printf("a = %d n", a);
printf("b = %d n", b);
}
}
20. for
// Demonstrate the for loop (loop.c).
#include <stdio.h>
main() {
int n;
for(n=10; n>0; n--)
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for(n=10; n>0; n--)
printf("tick %d n",n);
}
21. While loopWhile loopWhile loopWhile loop
While loop
The general form of while is as shown below:
initialize loop counter
while(test loop counter using a condition) {
statement block;
increment/decrement loop counter;
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increment/decrement loop counter;
}
The statements within the while loop would keep on getting
executed till the condition being tested remains true.
23. while
// Demonstrate the while loop (while.c).
#include <stdio.h>
main() {
int n = 10;
while(n > 0) {
printf("tick %d n",n);
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printf("tick %d n",n);
n--;
} // while
} // main
24. do-while loop
The general form of do-while
initialize loop counter
do
{
statement block;
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statement block;
increment/decrement loop counter;
} while(test loop counter using a condition);
25. dodododo----while loopwhile loopwhile loopwhile loop
// Demonstrate the do-while loop (dowhile.c).
#include <stdio.h>
main() {
int n = 10;
do {
printf("tick %d n",n);
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printf("tick %d n",n);
n--;
} while(n > 0);
} // main
26. While Vs do-while loops
There is a minor difference between the working of
while and do-while loops.
This difference is the place where the condition is tested.
The while tests the condition before executing any of the
statements within the while loop.
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statements within the while loop.
The do-while tests the condition after having executed
the statements within the loop.
Statements under do-while loop will get
executed atleast once and not so incase of while
loop
27. Nested LoopsNested LoopsNested LoopsNested Loops
Like all other programming languages, C allows loops to be nested.That is, one
loop may be inside another. For example, here is a program that nests for loops:
// Loops may be nested (nestedfor.c).
#include <stdio.h>
main() {
int i, j;
for(i=0; i<10; i++) {
Dept. of CS&E and IT, DBCET, Guwahati27
for(i=0; i<10; i++) {
for(j=i; j<10; j++)
printf(".");
printf("n");
}
}
28. JumpJumpJumpJump
C supports four jump statements:
break,
continue,
return
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goto.
These statements transfer control to another part
of your program.
29. breakbreakbreakbreak
In C, the break statement has two uses.
First, it terminates a statement
sequence in a switch statement.
Second, it can be used to exit a loop.
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Second, it can be used to exit a loop.
30. break statement
We often come across situations where we want to jump out
of a loop instantly, without waiting to get back to the
conditional test.
The keyword break allows us to do this.
When break is encountered inside any loop, control
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When break is encountered inside any loop, control
automatically passes to the first statement after the loop.
31. break
// Using break to exit a loop (break.c).
#include <stdio.h>
main() {
int i;
for(i=0; i<100; i++) {
Dept. of CS&E and IT, DBCET, Guwahati31
for(i=0; i<100; i++) {
if(i == 10) break; // terminate loop if i is 10
printf("i: %d n", i);
}
printf("Loop complete.");
}
32. break
// Using break to exit a while loop (break2.c).
#include <stdio.h>
main() {
int i = 0;
while(i < 100) {
if(i == 10) break; // terminate loop if i is 10
printf("i: %d n", i);
Dept. of CS&E and IT, DBCET, Guwahati32
printf("i: %d n", i);
i++;
}
printf("Loop complete.");
}
33. break statement example
main( ) { int i = 1 , j = 1 ;
while ( i++ <= 100 )
{
while ( j++ <= 200 )
{
In this program when j equals 150,
break takes the control outside
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if ( j == 150 )
break ;
else
printf ( "%d %dn", i, j ) ;
}
}
}
break takes the control outside
the inner while only, since it is
placed inside the inner while.
34. continuecontinuecontinuecontinue
continue go immediately to next iteration of loop
In while and do-while loops, a continue statement causes
control to be transferred directly to the conditional
expression that controls the loop.
In a for loop, control goes first to the iteration portion of
the for statement and then to the conditional expression.
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In a for loop, control goes first to the iteration portion of
the for statement and then to the conditional expression.
35. continue
// Demonstrate continue (continue.c).
#include <stdio.h>
main() {
int i;
for(i=0; i<10; i++) {
printf("%d ", i);
Dept. of CS&E and IT, DBCET, Guwahati35
printf("%d ", i);
if (i%2 == 0) continue;
printf("n");
}
}
36. returnreturnreturnreturn
The return statement is used to explicitly return from a
method.That is, it causes program control to transfer
back to the caller of the method.
The following example illustrates this point. Here,
return causes execution to return to the C, since it is the
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return causes execution to return to the C, since it is the
run-time system that calls main( ).
37. return
// Demonstrate return (return.c).
#include <stdio.h>
main() {
int t = 1;
printf("Before the return.");
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printf("Before the return.");
if(t==1) return; // return to caller
printf("This won't execute.");
}
38. goto
It is possible to jump to any statement within the same
function using goto.
A label is used to mark the destination of the jump.
goto label1;
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:
:
label1:
39. goto
// Using continue with a label (goto.c).
#include <stdio.h>
main() {
int i,j;
for (i=0; i<10; i++) {
for(j=0; j<10; j++) {
if(j > i) {
printf("n");
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printf("n");
goto outer;
}
printf(" %d", (i * j));
}
outer: printf(".. outer ..n");
}
}
