Decision making statements in C programming

Decision making
statements in C
1Presented by: Group-E (The Anonymous)
Bikash Dhakal
Bimal Pradhan
Bikram Bhurtel
Gagan Puri
Rabin BK

Introduction to decision making statements
Decision making statements in C
If statement
If….else statement
If….else if….else statement
Nested if statement
Switch statement
The conditional operator(? : )
GOTO statement
References
Queries
2

Introduction to decision making statement in C
Also known as control statements
Controls the flow of execution
Executes program until a specified condition is met
One of the most important parts in programming
3

Decision making statements in C
if statement
switch statement
Conditional operator statement
goto statement
4

If statement
The expression must evaluate to true or false.
The “statement” can be a group of statements in braces:
Syntax:
5
if(expression)
{
Statement 1;
Statement 2;
}

6
#include<stdio.h>
#include<conio.h>
main( )
{
int n ;
printf ( "Enter your age: " ) ;
scanf ("%d", &n ) ;
if ( n>=20 )
{
printf (“nYou are in your adulthood. ” ) ;
}
getch();
}
Enter any number: 25
You are in your adulthood.

If else statement
 An extension version of if statement.
 Generally in the form of if (test expression)
7
if (test expression)
{
true block statement(s)
}
else
{
false block statement(s)
}

Example
8
#include<stdio.h>
#include<conio.h>
main()
{
int age;
printf("n enter your age:");
scanf("%d",&age);
if(age>=18)
{
printf("eligible for citizenship");
}
else
{
printf("n NOT ELIGIBLE");
}
getch();
}
enter your age:13
NOT ELIGIBLE
enter your age:20
eligible for citizenship

If …else if…. else statement
 It is used to give series of decision
 Syntax:
9
if (condition)
{
//statement 1
}
else if (condition 2)
{
//statement 2
}
else
{
// statement when all condition are false
}

#include<stdio.h>
#include<conio.h>
#include<math.h>
void main()
{
float a,b,c,d,r1,r2;
printf("Enter coefficients a, b and c: ");
scanf("%f%f%f",&a,&b,&c);
d=b*b-4*a*c;
if(d==0)
{
r1=-b/(2*a);
printf("n Roots are equal and is %.3f",r1);
}
else if(d>0)
{
d=sqrt(d);
r1=(-b+d)/(2*a);
r2=(-b-d)/(2*a);
printf("nRoots are real and r1=%.3f, r2=%.3f",r1,r2);
}
else
{
d=sqrt(fabs(d));
printf("n Roots are imaginary");
printf("n r1=%.3f + i%.3f",-b/(2*a),d/(2*a));
printf("n r2=%.3f - i%.3f",-b/(2*a),d/(2*a));
}
getch();
10
//Program to find the roots of the quadratic equations ax^2+bx+c=0
Enter coefficients a, b, c: 1
2
1
Roots are equal and is -1.000

Nested if-else statement
New block of if-else statement defined
in existing if or else block statement.
Syntax:
11
if(condition)
{
if(condition)
{
statement
}
else
{
statement
}
}
else
{
statement
}

12
#include <stdio.h>
#include <conio.h>
void main( )
{
int a,b,c;
printf("Enter 3 numbers: n");
scanf("%d%d%d",&a,&b,&c);
if(a>b)
{
if( a > c)
{
printf(“%d is greatest“,a);
}
else
{
printf(“%d is greatest“,c);
}
}
else
{
if( b> c)
{
printf(“%d is greatest“,b);
}
else
{
printf(“%d is greatest“,c);
}
}
getch();
}
Using Nested-if statement to check greatest
number among three input numbers
Enter 3 numbers:
9
11
5
11 is greatest
Enter 3 numbers:
49
55
88
88 is greatest

 Multi-way decision statement
 Tests the value of a given variable against a list of case values
 when a match is found, a block of statements associated with that
case is executed.
13

switch (var)
{
case case value 1:
statements;
break;
case case value 2:
statements;
break;
…….
…….
case case value n:
default:
statements;
break;
}
Should be an integer or characters
Known as case labels and should be constants or
constant expressions
And should be end with semicolon
14

#include<stdio.h>
int main()
{
char operator;
float firstNumber,secondNumber;
printf("Enter an operator (+, -): ");
scanf("%c", &operator);
printf("Enter two operands: ");
scanf("%f %f",&firstNumber, &secondNumber);
switch(operator)
{
case '+':
printf("%f + %f = %f",firstNumber, secondNumber, firstNumber +
secondNumber);
break;
case '-':
printf("%f - %f = %f",firstNumber, secondNumber, firstNumber -
secondNumber);
break;
default:
printf("Error! operator is not correct");
}
return 0;
}
Enter an operator(+,-): -
Enter two operands: 6
4
6.000000 – 4.000000 = 2.000000
Enter an operator(+,-): /
Enter two operands: 9
3
Error! operator is not correct
15

The ?: operator
Known as conditional operator
Used for making two-way decisions
Syntax:
16
Conditional expression ? exp1: exp2

Example:
17
//If True first exp is executed
//If False second exp is executed
#include <stdio.h>
#include <conio.h>
#include <math.h>
void main()
{
int a;
printf("Enter a number: ");
scanf("%d",&a);
(a%2==0?printf("Even"):printf("Odd"));
getch();
}
Enter a number: 9
Odd
Enter a number: 8
Even

The GOTO statement
Rarely used statement
Provides an unconditional jump from ‘goto’ to a labelled statement
in the same function
Syntax:
Requires label to identify the place where the branch is to be made
18
goto label;
-------------
-------------
label;
statement;
label;
statement;
-------------
-------------
goto label;
Forward jump Backward jump

Example:
19
#include <stdio.h>
#include <conio.h>
#include <math.h>
void main()
{
float y,x;
read:
printf("nEnter a number: ");
scanf("%f",&y);
if(y<0) goto read;
x=sqrt(y);
printf("nSquare root of %f---->%fn",y,x);
goto read;
}
Enter a number: 9
Square root of 9.000000---->3.000000
Enter a number: 25
Square root of 25.000000---->5.000000

References:
Websites:
google.com
codecadamy.com
tutorialspoint.com
External sources:
Text book: Programming in ANSIC (E-Balagurusamy)
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Decision making statements in C programming

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