Lecture Computing for management - Chapter 25

Lecture 25 - Selection. In the previous lecture we have been covered algorithms and programs, in this chapter you will be able to understand: The if statement, the else statement, cascaded if, nested if, switch statement.

Lecture 25

Summary of previous lecture

 In the previous lecture we have been covered,

 A C programming language

 History of C

 C, A High level language

 How to get started with C.

 Basic Structure of a C program

 Data Storage and Data Types

 Variables, Keywords, identifiers, Assignment

Summary of previous lecture

 If team scored less than 250 runs, it will be

out of the tournament.

 If the temperature is greater than 50 degree

Celsius then wear light dress.

Conditions in C Programming

 Same if structure is used in c

programming to test the condition.

 It has two parts

 Conditional  or  antecedent  or  LHS  part and 

 Conclusion  or  action  or  consequent  or 

RHS  part.

The if statement

 Determines whether a statement or block is executed.

 Implements the selection instructions within an

algorithm.

 Decides what to do by evaluating a Boolean expression.

 If the expression is true (non-zero), the statement or

block is executed.

if ( expression )

statement

What is a statement?

 Statements are lines of instructions in our

programs ending with a semicolon (;).

 A compound statement or block is a series of statements surrounded by braces.

{ number = number + 1;

printf("%d\n", number);

}

• An  empty statement  is a single semicolon.

E.g.

Read in a number, and print it

#include <stdio.h>

/* Read in a number, and echo it

if it is odd */

int main() {

#include <stdio.h>

/* Read in a number, and echo it

if it is odd */

int main() {

int number;

printf("Enter an integer: "); scanf("%d", &number);

#include <stdio.h>

/* Read in a number, and echo it

if it is odd */

int main() {

int number;

printf("Enter an integer: "); scanf("%d", &number);

if (number % 2 != 0) {

printf("%d\n", number); }

#include <stdio.h>

/* Read in a number, and echo it

if it is odd */

int main() {

int number;

printf("Enter an integer: "); scanf("%d", &number);

if (number % 2 != 0) {

printf("%d\n", number); }

#include <stdio.h>

/* Read in a number, and echo it

if it is odd */

int main() {

int number;

printf("Enter an integer: "); scanf("%d", &number);

if (number % 2 != 0) {

printf("%d\n", number); }

Example: oddnum.c 

#include <stdio.h>

/* Read in a number, and echo it

if it is odd */

int main() {

int number;

printf("Enter an integer: "); scanf("%d", &number);

if (number % 2 != 0) {

printf("%d\n", number); }

Notes on if

 Which of the following code fragments are equivalent?

if (number % 2 != 0) {

printf("%d", number);

} printf(” is odd\n");

if (number % 2 != 0) printf("%d", number);

printf(” is odd\n");

if (number % 2 != 0) {

Notes on if

 Which of the following code fragments are equivalent?

if (number % 2 != 0) {

printf("%d", number);

}

printf(” is odd\n");

if (number % 2 != 0) printf("%d", number);

printf(” is odd\n");

if (number % 2 != 0) {

Notes on if

 Which of the following code fragments are equivalent?

if (number % 2 != 0)

{ printf("%d", number);

Notes on if

 Common mistake

if (number % 2 != 0);

{ printf("%d is an odd ", number); }

printf("number\n");

Notes on if

 Common mistake

if (number % 2 != 0) ;

{ printf("%d is an odd ", number); }

printf("number\n");

No semi­

colon here!

The semicolon is an  empty statement.

Notes on if

 Common mistake

if (number = 0) {

printf("%d\n", number); }

printf("%d\n", number);

Notes on if

 Common mistake

if (number = 0) {

printf("%d\n", number); }

printf("%d\n", number);

Should be  ==

The else statement

 Can only occur after an if statement

 Is only executed when the if block does

#include <stdio.h>

/* Determine whether an input number

is odd or even */

main() {

int number;

printf("Enter an integer: ");

scanf("%d", &number);

if (number % 2 != 0) {

printf("%d is an odd number\n", number);

}

}

Read in a number, and

determine if it’s odd or

#include <stdio.h>

/* Determine whether an input number

is odd or even */

main() {

int number;

printf("Enter an integer: ");

scanf("%d", &number);

if (number % 2 != 0) {

printf("%d is an odd number\n", number);

} else { printf("%d is an even number\n", number);

}

}

Example: oddeven.c 

Read in a number, and

determine if it’s odd or

#include <stdio.h>

/* Determine whether an input number

is odd or even */

main() {

int number;

printf("Enter an integer: ");

scanf("%d", &number);

if (number % 2 != 0) {

printf("%d is an odd number\n", number);

} else { printf("%d is an even number\n", number);

} }

Example: oddeven.c 

Read in a number, and

determine if it’s odd or

#include <stdio.h>

/* Determine whether an input number

is odd or even */

main() {

int number;

printf("Enter an integer: ");

scanf("%d", &number);

if (number % 2 != 0) {

printf("%d is an odd number\n", number);

} else { printf("%d is an even number\n", number);

} }

Example: oddeven.c 

Read in a number, and

determine if it’s odd or

Output of a program

Determine the number of days in

a given month:

30 days = September,

April, June and November.

All the rest have 31,

Excepting February alone,

Which have 28 days clear,

And 29 in each leap year.

output “Enter an integer” input month

if (month is September,

or April,

or June,

or November) then

{ output “30 days”

} else if (month is February) {

output “28 or 29 days” }

else { output “31 days”

}

int main() {

return 0; }

April, June and November;

All the rest have 31,

Excepting February alone,

And that has 28 days clear

And 29 in each leap year.

\*************************/

const int September = 9;

const int April = 4;

const int June = 6;

const int November = 11;

const int February = 2;

int main() {

April, June and November;

All the rest have 31,

Excepting February alone,

And that has 28 days clear

And 29 in each leap year.

\*************************/

const int September = 9;

const int April = 4;

const int June = 6;

const int November = 11;

const int February = 2;

int main() {

30 days hath September,

April, June and November;

All the rest have 31,

Excepting February alone,

And that has 28 days clear

And 29 in each leap year.

\*************************/

const int September = 9;

const int April = 4;

const int June = 6;

const int November = 11;

const int February = 2;

#include <stdio.h>

/*************************\

Determine the number of days

in a given month:

30 days hath September,

April, June and November;

All the rest have 31,

Excepting February alone,

And that has 28 days clear

And 29 in each leap year.

\*************************/

const int September = 9;

const int April = 4;

const int June = 6;

const int November = 11;

const int February = 2;

int main() {

int main() {

printf("30 days\n");

} else if (month==February) {

30 days hath September,

April, June and November;

All the rest have 31,

Excepting February alone,

And that has 28 days clear

And 29 in each leap year.

\*************************/

const int September = 9;

const int April = 4;

const int June = 6;

const int November = 11;

const int February = 2;

int main() {

printf("30 days\n");

} else if (month==February) {

printf("28 or 29 days\n");

} else { printf("31 days\n");

30 days hath September,

April, June and November;

All the rest have 31,

Excepting February alone,

And that has 28 days clear

And 29 in each leap year.

\*************************/

const int September = 9;

const int April = 4;

const int June = 6;

const int November = 11;

const int February = 2;

int main() {

printf("30 days\n");

} else if (month==February) {

printf("28 or 29 days\n");

} else { printf("31 days\n");

30 days hath September,

April, June and November;

All the rest have 31,

Excepting February alone,

And that has 28 days clear

And 29 in each leap year.

\*************************/

const int September = 9;

const int April = 4;

const int June = 6;

const int November = 11;

const int February = 2;

“Default” block.

int main() {

printf("30 days\n");

} else if (month==February) {

printf("28 or 29 days\n");

} else { printf("31 days\n");

} return 0;

30 days hath September,

April, June and November;

All the rest have 31,

Excepting February alone,

And that has 28 days clear

And 29 in each leap year.

\*************************/

const int September = 9;

const int April = 4;

const int June = 6;

const int November = 11;

const int February = 2;

Notes on Cascaded if

if (letter >= ’a’) {

printf(“S1\n”);

} else if (letter <= ’z’) {

printf(“S2\n”);

} else if (letter >= ’A’) {

printf(“S3\n”);

} else if (letter <= ’Z’) {

Notes on Cascaded if

if (letter >= ’a’) {

printf(“S1\n”);

} else if (letter <= ’z’) {

printf(“S2\n”);

} else if (letter >= ’A’) {

printf(“S3\n”);

} else if (letter <= ’Z’) {

Switch Statement

multi- Multi-way selection chooses among

several alternatives C programming can use switch statement for multi-way

selection.

The Switch statement

Expression here is user entered variable value

The Switch statement

case is a default word.

The Switch statement Expression is matched with the constant of each

case, wherever it is matched, next statements

are executed

The Switch statement

If the expression doesn’t matched with any case

default is executed.

Closed switch resembles

executed case

Switch statement

printFlag is a variable

In order to stop next case to

be automatically executed,

break

statement has been used.

Multiple cases being executed together

Summary of switch Statement Rules

Develop the program for assigning the grades using if and switch

statements separately.

int main() {

int marks;

printf("%s", "Enter yours Marks"); scanf("%d",&marks);

switch(marks) {

case 100:case 99:case 98:case 97:case 96:case 95:case 94:

case 93:case 92:case 91:case 90:

printf("%s", "You got A grade");

break;

Remember you need constants

here, so explicitly write

all statements for which this

case may be executed.

Switch statement

case 89:case 88:case 87:case 86:case 85:case 84: case 83:case 82:case 81:case 80:

printf("%s", "You got B grade");

Alternative If statements

int main() {

int marks;

printf("%s", "Enter yours Marks"); scanf("%d",&marks);

if (marks >=90) {

printf("%s", "you got A grade");

}

else if (marks >=80)

User inputs marks

First Check, if true

rest of the statements will not be executed

If first check is false,

this statement will be

checked and so on!

printf("%s", "you got B grade"); }

else if (marks >=70) {

printf("%s", "you got c grade"); }

else if (marks >=60) {

printf("%s", "you got D grade"); }

else printf("%s", "you got F grade");

 If conditions are used to execute

statement or a group of statements based upon logically tested values.

 Alternative to if condition is switch

statement.

 Both if and switch statements form logical

structure of a program.