 Decision making structures require that the programmer specifies one or

more conditions to be evaluated or tested by the program, along with a

statement or statements to be executed if the condition is determined to be
true, and optionally, other statements to be executed if the condition is
determined to be false.
 Show below is the general form of a typical decision making structure
found in most of the programming languages −
 C programming language assumes any non-zero and non-null values
as true, and if it is either zero or null, then it is assumed as false value.
 C programming language provides the following types of decision making
statements.
Sr.No. Statement & Description

1
if statement
An if statement consists of a boolean expression followed by one or more
statements.

2
if...else statement
An if statement can be followed by an optional else statement, which executes
when the Boolean expression is false.

3
nested if statements
You can use one if or else if statement inside another if or else if statement(s).

4
switch statement
A switch statement allows a variable to be tested for equality against a list of
values.

5
nested switch statements
You can use one switch statement inside another switch statement(s).
Simple if statement

The general form of a simple if statement is,

if(expression)

statement inside;

statement outside;
If the expression returns true, then the statement-inside will be executed,
otherwise statement-inside is skipped and only the statement-outside is
executed.

Example:

#include <stdio.h>

void main( )

int x, y;

x = 15;

y = 13;

if (x > y )

printf("x is greater than y");

x is greater than y

if...else statement

The general form of a simple if...else statement is,

if(expression)

{
 statement block1;

else

statement block2;

If the expression is true, the statement-block1 is executed, else statement-

block1 is skipped and statement-block2 is executed.

Example:

#include <stdio.h>

void main( )

int x, y;

x = 15;

y = 18;

if (x > y )

printf("x is greater than y");

else

{
 printf("y is greater than x");

y is greater than x

Nested if....else statement

The general form of a nested if...else statement is,

if( expression )

if( expression1 )

statement block1;

else

statement block2;

else

statement block3;
}

if expression is false then statement-block3 will be executed, otherwise the

execution continues and enters inside the first if to perform the check for the
next if block, where if expression 1 is true the statement-block1 is executed
otherwise statement-block2 is executed.

Example:

#include <stdio.h>

void main( )

int a, b, c;

printf("Enter 3 numbers...");

scanf("%d%d%d",&a, &b, &c);

if(a > b)

if(a > c)

printf("a is the greatest");

else

printf("c is the greatest");

}
 }

else

if(b > c)

printf("b is the greatest");

else

printf("c is the greatest");

else if ladder
The general form of else-if ladder is,

if(expression1)

statement block1;

else if(expression2)
{

statement block2;

else if(expression3 )

statement block3;

else

default statement;

The expression is tested from the top(of the ladder) downwards. As soon as
a true condition is found, the statement associated with it is executed.

Example :

#include <stdio.h>

void main( )

int a;

printf("Enter a number...");

scanf("%d", &a);

if(a%5 == 0 && a%8 == 0)

{
 printf("Divisible by both 5 and 8");

else if(a%8 == 0)

printf("Divisible by 8");

else if(a%5 == 0)

printf("Divisible by 5");

else

printf("Divisible by none");

Points to Remember
In if statement, a single statement can be included without enclosing it into curly
braces { ... }

1. int a = 5;

2. if(a > 4)

printf("success");
 No curly braces are required in the above case, but if we have more than
one statement inside if condition, then we must enclose them inside curly
braces.
3. == must be used for comparison in the expression of if condition, if you
use = the expression will always return true, because it performs
assignment not comparison.
4. Other than 0(zero), all other values are considered as true.

5. if(27)

printf("hello");

In above example, hello will be printed.

Switch statement in C
 When you want to solve multiple option type problems, for example:
Menu like program, where one value is associated with each option
and you need to choose only one at a time, then, switch statement is
used.
 Switch statement is a control statement that allows us to choose only
one choice among the many given choices. The expression
in switch evaluates to return an integral value, which is then
compared to the values present in different cases. It executes that
block of code which matches the case value. If there is no match,
then default block is executed(if present). The general form
of switch statement is,
switch(expression)
{
case value-1:
block-1;
break;
case value-2:
block-2;
break;
case value-3:
block-3;
break;
case value-4:
block-4;
break;
default:
default-block;
break;
}
 Rules for using switch statement
The expression (after switch keyword) must yield an integer value i.e the
expression should be an integer or a variable or an expression that evaluates
to an integer.
 The case label values must be unique.
 The case label must end with a colon(:)
 The next line, after the case statement, can be any valid C statement.

Points to Remember

1. We don't use those expressions to evaluate switch case, which may return
floating point values or strings or characters.
2. break statements are used to exit the switch block. It isn't necessary to
use break after each block, but if you do not use it, then all the
consecutive blocks of code will get executed after the matching block.

3. int i = 1;

4. switch(i)

5. {

6. case 1:

7. printf("A"); // No break

8. case 2:

9. printf("B"); // No break

10. case 3:

11. printf("C");

12. break;

A B C
 The output was supposed to be only A because only the first case matches,
but as there is no break statement after that block, the next blocks are
executed too, until it a break statement in encountered or the execution
reaches the end of the switch block.

13. default case is executed when none of the mentioned case matches
the switch expression. The default case can be placed anywhere in
the switch case. Even if we don't include the default case, switch statement
works.
14. Nesting of switch statements are allowed, which means you can
have switch statements inside another switch block. However,
nested switch statements should be avoided as it makes the program more
complex and less readable.

C break statement
 The break is a keyword in C which is used to bring the program control
out of the loop. The break statement is used inside loops or switch
statement. The break statement breaks the loop one by one, i.e., in the
case of nested loops, it breaks the inner loop first and then proceeds to
outer loops. The break statement in C can be used in the following two
scenarios:
 With switch case
 With loop

Syntax:
1. //loop or switch case
2. break;
Flowchart of break in c
 Example
1. #include<stdio.h>
2. #include<stdlib.h>
3. void main ()
4. {
5. int i;
6. for(i = 0; i<10; i++)
7. {
8. printf("%d ",i);
9. if(i == 5)
10. break;
11. }
12. printf("came outside of loop i = %d",i);
13.
14. }

Output

0 1 2 3 4 5 came outside of loop i = 5

C – Continue statement
15. Example: continue statement inside for loop
16. #include <stdio.h>
17. int main()
18. {
19. for (int j=0; j<=8; j++)
20. {
21. if (j==4)
22. {
23. /* The continue statement is encountered when
24. * the value of j is equal to 4.
25. */
26. continue;
27. }
28.
29. /* This print statement would not execute for the
30. * loop iteration where j ==4 because in that case
31. * this statement would be skipped.
32. */
33. printf("%d ", j);
34. }
35. return 0;
36. }
37. Output:
38. 0 1 2 3 5 6 7 8

The ? : Operator
We have covered conditional operator ? : in the previous chapter which can be
used to replace if...else statements. It has the following general form −
Exp1 ? Exp2 : Exp3;
Where Exp1, Exp2, and Exp3 are expressions. Notice the use and placement of
the colon.
The value of a ? expression is determined like this −
 Exp1 is evaluated. If it is true, then Exp2 is evaluated and becomes the
value of the entire ? expression.
  If Exp1 is false, then Exp3 is evaluated and its value becomes the value of
the expression.
Goto Statement
A goto statement in C programming provides an unconditional jump from the
'goto' to a labeled statement in the same function.
NOTE − Use of goto statement is highly discouraged in any programming
language because it makes difficult to trace the control flow of a program,
making the program hard to understand and hard to modify. Any program that
uses a goto can be rewritten to avoid them.
Syntax
The syntax for a goto statement in C is as follows −
goto label;
..
.
label: statement;
Here label can be any plain text except C keyword and it can be set anywhere
in the C program above or below to goto statement.
Flow Diagram
Example
#include <stdio.h>

int main () {

/* local variable definition */

int a = 10;

/* do loop execution */
LOOP:do {

if( a == 15) {
/* skip the iteration */
a = a + 1;
goto LOOP;
}

printf("value of a: %d\n", a);

a++;

}
while( a < 20 );
return 0;
}

When the above code is compiled and executed, it produces the following result
value of a: 10
value of a: 11
value of a: 12
value of a: 13
value of a: 14
value of a: 16
value of a: 17
value of a: 18
value of a: 19

Loops in C
Loops in programming come into use when we need to repeatedly execute a block
of statements. For example: Suppose we want to print “Hello World” 10 times.
This can be done in two ways as shown below:
An iterative method to do this is to write the printf() statement 10 times.
Program
// C program to illustrate need of loops
#include <stdio.h>
int main()
{
printf( "Hello World\n");
printf( "Hello World\n");
printf( "Hello World\n");
printf( "Hello World\n");
printf( "Hello World\n");
printf( "Hello World\n");
printf( "Hello World\n");
printf( "Hello World\n");
printf( "Hello World\n");
printf( "Hello World\n");
return 0;
}

Output:
Hello World
Hello World
Hello World
Hello World
Hello World
Hello World
Hello World
Hello World
Hello World
Hello World

Using Loops
In Loop, the statement needs to be written only once and the loop will be executed
10 times as shown below.
 In computer programming, a loop is a sequence of instructions that is
repeated until a certain condition is reached.
 An operation is done, such as getting an item of data and changing it, and
then some condition is checked such as whether a counter has reached a
prescribed number.
 Counter not Reached: If the counter has not reached the desired number,
the next instruction in the sequence returns to the first instruction in the
sequence and repeat it.
 Counter reached: If the condition has been reached, the next instruction
“falls through” to the next sequential instruction or branches outside the
loop.
There are mainly two types of loops:
 Entry Controlled loops: In this type of loops the test condition is tested
before entering the loop body. For Loop and While Loop are entry
controlled loops.
 Exit Controlled Loops: In this type of loops the test condition is tested or
evaluated at the end of loop body. Therefore, the loop body will execute
atleast once, irrespective of whether the test condition is true or false. do –
while loop is exit controlled loop.
for Loop
A for loop is a repetition control structure which allows us to write a loop that
is executed a specific number of times. The loop enables us to perform n number
of steps together in one line.
Syntax:
for (initialization expr; test expr; update expr)
{
// body of the loop
// statements we want to execute
}
In for loop, a loop variable is used to control the loop. First initialize this loop
variable to some value, then check whether this variable is less than or greater
than counter value. If statement is true, then loop body is executed and loop
variable gets updated . Steps are repeated till exit condition comes.
  Initialization Expression: In this expression we have to initialize the loop
counter to some value. for example: int i=1;
 Test Expression: In this expression we have to test the condition. If the
condition evaluates to true then we will execute the body of loop and go
to update expression otherwise we will exit from the for loop. For
example: i <= 10;
 Update Expression: After executing loop body this expression
increments/decrements the loop variable by some value. for example:
i++;
Equivalent flow diagram for loop :

Example:
// C program to illustrate for loop
#include <stdio.h>
int main()
{
int i=0;
for (i = 1; i <= 10; i++)
{
printf( "Hello World\n");
}
return 0;
}
Output:
Hello World
Hello World
Hello World
Hello World
Hello World
Hello World
Hello World
Hello World
Hello World
Hello World
Nested Loops in C
 C supports nesting of loops in C. Nesting of loops is the feature in C that
allows the looping of statements inside another loop. Let's observe an
example of nesting loops in C.
 Any number of loops can be defined inside another loop, i.e., there is no
restriction for defining any number of loops. The nesting level can be
defined at n times.
Syntax of Nested loop

Outer_loop
{
Inner_loop
{
// inner loop statements.
}
// outer loop statements.
}

Nested for loop

The nested for loop means any type of loop which is defined inside the 'for' loop.

for (initialization; condition; update)

{
for(initialization; condition; update)
{
// inner loop statements.
}
// outer loop statements.
}

Example of nested for loop

#include <stdio.h>
int main()
{
int n;// variable declaration
printf("Enter the value of n :");
// Displaying the n tables.
for(int i=1;i<=n;i++) // outer loop
{
for(int j=1;j<=10;j++) // inner loop
{
printf("%d\t",(i*j)); // printing the value.
printf("\n");
}
Explanation of the above code

o First, the 'i' variable is initialized to 1 and then program control passes to the
i<=n.
o The program control checks whether the condition 'i<=n' is true or not.
o If the condition is true, then the program control passes to the inner loop.
o The inner loop will get executed until the condition is true.
o After the execution of the inner loop, the control moves back to the update of
the outer loop, i.e., i++.
o After incrementing the value of the loop counter, the condition is checked
again, i.e., i<=n.
o If the condition is true, then the inner loop will be executed again.
o This process will continue until the condition of the outer loop is true.

Output:

While Loop
 While studying for loop we have seen that the number of iterations is
known beforehand, i.e. the number of times the loop body is needed to be
executed is known to us. while loops are used in situations where we do
not know the exact number of iterations of loop beforehand. The loop
execution is terminated on the basis of test condition.
 We have already stated that a loop is mainly consisted of three statements
– initialization expression, test expression, update expression. The syntax
of the three loops – For, while and do while mainly differs on the
placement of these three statements.
Syntax:
Initialization expression;
while (test_expression)
{
// statements
update_expression;
}
Flow Diagram:

Example:
// C program to illustrate while loop
#include <stdio.h>
int main()
{
 // initialization expression
int i = 1;
// test expression
while (i < 6)
{
printf( "Hello World\n");
// update expression
i++;
}
return 0;
}
Output:
Hello World
Hello World
Hello World
Hello World
Hello World
do while loop
In do while loops also the loop execution is terminated on the basis of test
condition. The main difference between do while loop and while loop is in do
while loop the condition is tested at the end of loop body, i.e do while loop is
exit controlled whereas the other two loops are entry controlled loops.
Note: In do while loop the loop body will execute at least once irrespective of
test condition.

Syntax:
initialization expression;
do
{
// statements
 update_expression;
} while (test_expression);
Note: Notice the semi – colon(“;”) in the end of loop.
Flow Diagram:

Example:
// C program to illustrate do-while loop
#include <stdio.h>
int main()
{
int i = 2; // Initialization expression
 do
{
// loop body
printf( "Hello World\n");
// update expression
i++;
} while (i < 1); // test expression
return 0;
}
Output:
Hello World
In the above program the test condition (i<1) evaluates to false. But still as the
loop is exit – controlled the loop body will execute once.
Declaring Arrays
 To declare an array in C, a programmer specifies the type of the elements
and the number of elements required by an array as follows −
type arrayName [ arraySize ];
 This is called a single-dimensional array. The arraySize must be an integer
constant greater than zero and type can be any valid C data type. For
example, to declare a 10-element array called balance of type double, use
this statement −
double balance[10];
 Here balance is a variable array which is sufficient to hold up to 10 double
numbers.

Initializing Arrays
 You can initialize an array in C either one by one or using a single statement
as follows −
double balance[5] = {1000.0, 2.0, 3.4, 7.0, 50.0};
 The number of values between braces { } cannot be larger than the number
of elements that we declare for the array between square brackets [ ].
  If you omit the size of the array, an array just big enough to hold the
initialization is created. Therefore, if you write −
double balance[] = {1000.0, 2.0, 3.4, 7.0, 50.0};
 You will create exactly the same array as you did in the previous example.
Following is an example to assign a single element of the array −
balance[4] = 50.0;
 The above statement assigns the 5th element in the array with a value of
50.0. All arrays have 0 as the index of their first element which is also called
the base index and the last index of an array will be total size of the array
minus 1. Shown below is the pictorial representation of the array we
discussed above −

Accessing Array Elements

 An element is accessed by indexing the array name. This is done by placing
the index of the element within square brackets after the name of the array.
For example −
double salary = balance[9];
The above statement will take the 10th element from the array and assign the value
to salary variable. The following example shows how to use all the three above
mentioned concepts viz. declaration, assignment, and accessing arrays −
#include <stdio.h>
int main ()
{
int n[ 10 ]; /* n is an array of 10 integers */
int i,j;
/* initialize elements of array n to 0 */
for ( i = 0; i < 10; i++ ) {
n[ i ] = i + 100; /* set element at location i to i + 100 */
}
/* output each array element's value */
for (j = 0; j < 10; j++ ) {
printf("Element[%d] = %d\n", j, n[j] );
}
return 0;
}
When the above code is compiled and executed, it produces the following result −
Element[0] = 100
Element[1] = 101
Element[2] = 102
Element[3] = 103
Element[4] = 104
Element[5] = 105
Element[6] = 106
Element[7] = 107
Element[8] = 108
Element[9] = 109
Arrays in Detail
Arrays are important to C and should need a lot more attention. The following
important concepts related to array should be clear to a C programmer −

S.No. Concept & Description

1 Multi-dimensional arrays

C supports multidimensional arrays. The simplest form of the multidimensional

array is the two-dimensional array.

2 Passing arrays to functions

You can pass to the function a pointer to an array by specifying the array's name
without an index.

3 Return array from a function

C allows a function to return an array.

4 Pointer to an array

You can generate a pointer to the first element of an array by simply specifying
the array name, without any index.
One-dimensional array

Conceptually you can think of a one-dimensional array as a row, where elements

are stored one after another.
Syntax: datatype array_name[size];

datatype: It denotes the type of the elements in the array.

array_name: Name of the array. It must be a valid identifier.

size: Number of elements an array can hold. here are some example of array
declarations:

int num[100];
float temp[20];
char ch[50];

num is an array of type int, which can only store 100 elements of type int.
temp is an array of type float, which can only store 20 elements of type float.
ch is an array of type char, which can only store 50 elements of type char.

Note: When an array is declared it contains garbage values.

The individual elements in the array:

num[0], num[1], num[2], ....., num[99]

temp[0], temp[1], temp[2], ....., temp[19]
ch[0], ch[1], ch[2], ....., ch[49]

Two dimensional (2D) arrays in C programming with example

An array of arrays is known as 2D array. The two dimensional (2D) array in C

programming is also known as matrix. A matrix can be represented as a table of
rows and columns. Before we discuss more about two Dimensional array lets have
a look at the following C program.
Simple Two dimensional(2D) Array Example
For now don’t worry how to initialize a two dimensional array, we will discuss that
part later. This program demonstrates how to store the elements entered by user in a
2d array and how to display the elements of a two dimensional array.
#include<stdio.h>
int main()
{
/* 2D array declaration*/
int disp[2][3];
/*Counter variables for the loop*/
int i, j;
for(i=0; i<2; i++) {
for(j=0;j<3;j++) {
printf("Enter value for disp[%d][%d]:", i, j);
scanf("%d", &disp[i][j]);
}
}
//Displaying array elements
printf("Two Dimensional array elements:\n");
for(i=0; i<2; i++) {
for(j=0;j<3;j++) {
printf("%d ", disp[i][j]);
if(j==2){
printf("\n");
}
}
}
return 0;
}
Output:
Enter value for disp[0][0]:1
Enter value for disp[0][1]:2
Enter value for disp[0][2]:3
Enter value for disp[1][0]:4
Enter value for disp[1][1]:5
Enter value for disp[1][2]:6
Two Dimensional array elements:
123
456
Multi Dimensional Array in C
In C Programming Language, by placing n number of brackets [ ], we can declare n-
dimensional array where n is dimension number. For example,
int a[2][3][4] = Three Dimensional Array

int a[2][2][3][4] = Four Dimensional Array

Syntax of a Multi Dimensional Array in C Programming

Data_Type Array_Name[Tables][Row_Size][Column_Size]

 Data_type: It will decide the type of elements it will accept. For example, If
we want to store integer values then we declare the Data Type as int, If we
want to store Float values then we declare the Data Type as float etc
 Array_Name: This is the name you want to give it to Multi Dimensional array
in C.
 Tables: It will decide the number of tables an array can accept. Two
Dimensional Array is always a single table with rows and columns. In
contrast, Multi Dimensional array in C is more than 1 table with rows and
columns.
 Row_Size: Number of Row elements an array can store. For example,
Row_Size =10, the array will have 10 rows.
 Column_Size: Number of Column elements an array can store. For example,
Column_Size = 8, the array will have 8 Columns.
We can calculate the maximum number of elements in a Three Dimensional using:
[Tables] * [Row_Size] * [Column_Size]

C Multi Dimensional Array Initialization

int Employees[2][4][3] = { { {10, 20, 30}, {15, 25, 35}, {22, 44, 66}, {33, 55, 77}
}, { {1, 2, 3}, {5, 6, 7}, {2, 4, 6}, {3, 5, 7} }

 Here, We have 2 tables and the 1st table holds 4 Rows * 3 Columns, and the
2nd table also holds 4 Rows * 3 Columns
  The first three elements of the first table will be 1st row, the second three
elements will be 2nd row, the next three elements will be 3rdrow, and the last
3 elements will be 4th row. Here we divided them into 3 because our column
size = 3, and we surrounded each row with curly braces ({}). It is always good
practice to use the curly braces to separate the rows.

We can also write

int Employees[2][4][ ] = { { {10, 20, 30}, {15, 25, 35}, {22, 44, 66}, {33, 55,
77} },
{ {1, 2, 3}, {5, 6, 7}, {2, 4, 6}, {3, 5, 7} }

};
Third Approach for Multi Dimensional Array in C
int Employees[2][4][3] = { { { 10 }, {15, 25}, {22, 44, 66}, {33, 55, 77} },

{ {1, 2, 3}, {5, 6, 7}, {2, 4, 6}, {3, 5, 7} }

};
Here, we declared Employees array with row size = 4 and column size = 3.
But we only assigned 1 column in the 1st row and 2 columns in the 2nd row
of the first table. In these situations, the remaining values will assign to default
values(0inthiscase).

Accessing Multi Dimensional Array in C

We can access the C Multi Dimensional array elements using indexes. Index starts
at 0 and ends at n-1, where n is the size of a row or column.
For example, if an Array_name[4][8][5] will store 8-row elements and 5 column
elements in each table where table size = 4. To access 1st value of the 1st table, use
Array_name[0][0][0], to access 2nd row 3rd column value of the 3rd table then use
Array_name[2][1][2] and to access the 8th row 5th column of the last table (4th
table), use Array_name[3][7][4]. Lets see the example of C Multi Dimensional
Array for better understanding:

int Employees[2][4][3] = { {10, 20, 30}, {15, 25, 35}, {22, 44, 66}, {33, 55, 77} },
{ {1, 2, 3}, {5, 6, 7}, {2, 4, 6}, {3, 5, 7} }
};

//To Access the values in the Employees[2][4][3] array

//Accessing First Table Rows & Columns

Printf("%d", Employees[0][0][0]) = 10

Printf("%d", Employees[0][0][1]) = 20
Printf("%d", Employees[0][0][2]) = 30

Printf("%d", Employees[0][1][0]) = 15

Printf("%d", Employees[0][1][1]) = 25

Printf("%d", Employees[0][1][2]) = 35

Printf("%d", Employees[0][2][0]) = 22

Printf("%d", Employees[0][2][1]) = 44

Printf("%d", Employees[0][2][2]) = 66

Printf("%d", Employees[0][3][0]) = 33

Printf("%d", Employees[0][3][1]) = 55

Printf("%d", Employees[0][3][2]) = 77

//Accessing Second Table Rows & Columns

Printf("%d", Employees[1][0][0]) = 1

Printf("%d", Employees[1][0][1]) = 2

Printf("%d", Employees[1][0][2]) = 3

Printf("%d", Employees[1][1][0]) = 5

Printf("%d", Employees[1][1][1]) = 6

Printf("%d", Employees[1][1][2]) = 7

Printf("%d", Employees[1][2][0]) = 2

Printf("%d", Employees[1][2][1]) = 4

Printf("%d", Employees[1][2][2]) = 6

Printf("%d", Employees[1][3][0]) = 3

Printf("%d", Employees[1][3][1]) = 5

Printf("%d", Employees[1][3][2]) = 7