C Programming: Control Structure

Chapter 3:
Control Flow/ Structure
PREPARED BY: MS. SA SOKNGIM

Content
1. Decision Making
2. Loops
3. Break and Continue Statement
4. Switch… case Statement
5. goto and label Statement

1. Decision Making
 Decision making is used to
specify the order in which
statements are executed.
• Decision making in a C program using:
• if statement
• if…else statement
• if…else if…else statement
• nested if...else statement
• Switch case Statement

1.1 if statement
if (testExpression)
{
// statements
}

Example: if statement
// Program to display a number if user enters negative number
// If user enters positive number, that number won't be displayed
#include <stdio.h>
int main()
{
int number;
printf("Enter an integer: ");
scanf("%d", &number);
// Test expression is true if number is less than 0
if (number < 0) {
printf("You entered %d.n", number);
}
printf("The if statement is easy.");
return 0;
}

1.2 if...else statement
 The if...else statement executes some code if the test expression
is true (nonzero) and some other code if the test expression is
false (0).
Syntax of if...else
if (testExpression) {
// codes inside the body of if
}else {
// codes inside the body of else
}

Example: if...else statement
// Program to check whether an integer entered by the user is odd or even
#include <stdio.h>
int main()
{
int number;
scanf("%d",&number);
// True if remainder is 0
if( number%2 == 0 )
printf("%d is an even integer.",number);
else
printf("%d is an odd integer.",number);
return 0;
}

1.3 if...else if....else Statement
 The if...else statement executes two different codes
depending upon whether the test expression is true or false.
Sometimes, a choice has to be made from more than 2
possibilities.
 The if...else if…else statement allows you to check for
multiple test expressions and execute different codes for
more than two conditions.

Syntax of if...else if....else statement.
if (testExpression1) {
// statements to be executed if testExpression1 is true
} else if(testExpression2) {
// statements to be executed if testExpression1 is false and
testExpression2 is true
} else if (testExpression 3) {
// statements to be executed if testExpression1 and
testExpression2 is false and testExpression3 is true
} else {
// statements to be executed if all test expressions are false
}

Example: if...else if....else statement
// Program to relate two integers
using =, > or <
#include <stdio.h>
int main(){
int number1, number2;
printf("Enter two integers: ");
scanf("%d %d", &number1,
&number2);
//checks if two integers are
equal.
if(number1 == number2){
printf("Result: %d = %d“,
number1,number2);
}
//checks if number1 is greater than
number2.
else if (number1 > number2) {
printf("Result: %d > %d",
number1, number2);
}
// if both test expression is false
else {
printf("Result: %d < %d",
number1, number2);
}
return 0;
}

1.4 Nested if else statement
 Nested if else statement is same like if else
statement, where new block of if else statement is
defined in existing if or else block statement.
 Used when user want to check more than one
conditions at a time.

Syntax of Nested If else Statement
if(condition is true){
if(condition is true){
statement;
}else{
statement;
}
}else{
statement;
}

Example of Nested if else Statement
#include <stdio.h>
void main(){
char username;
int password;
printf("Username:");
scanf("%c",&username);
printf("Password:");
scanf("%d",&password);
if(username=='a'){
if(password==12345){
printf("Login successful");
}else{
printf("Password is incorrect, Try again.");
}
}else{
printf("Username is incorrect, Try again.");
}
}

2. Loops
 Loops are used in programming to repeat a specific block until some end
condition is met.
 There are three loops in C programming:
o for loop
o while loop
o do...while loop
o Nested loops

2.1 for Loop
 The syntax of a for loop is:
for (initializationStatement; testExpression; updateStatement)
{
// codes
}

Example: for loop
// Program to calculate the sum of
first n natural numbers
// Positive integers 1,2,3...n are
known as natural numbers
#include <stdio.h>
int main(){
int n, count, sum = 0;
printf("Enter a positive integer: ");
scanf("%d", &n);
// for loop terminates when n is less
than count
for(count = 1; count <= n; ++count)
{
sum += count;
}
printf("Sum = %d", sum);
return 0;
}

2.2 while loop
 The syntax of a while loop is:
while (testExpression)
{
//codes
}

Example: while loop
/ Program to find factorial of
a number
// For a positive integer n,
factorial = 1*2*3...n
#include <stdio.h>
int main(){
int number;
long factorial;
scanf("%d",&number);
factorial = 1;
// loop terminates when number is less
than or equal to 0
while (number > 0) {
// factorial = factorial*number;
factorial *= number;
--number;
}
printf("Factorial= %lld", factorial);
return 0;
}

2.3 do...while loop
 The do..while loop is similar to the while loop with one
important difference.
 The body of do...while loop is executed once, before
checking the test expression.
 The do...while loop is executed at least once.

do...while loop Syntax
The syntax of a do while loop is:
do
{
// codes
}
while (testExpression);

Example: do...while loop
// Program to add numbers until user enters zero
#include <stdio.h>
int main() {
double number, sum = 0;
// loop body is executed at least once
do{
printf("Enter a number: ");
scanf("%lf", &number);
sum += number;
}while(number != 0.0);
printf("Sum = %.2lf",sum);
return 0;
}

2.4 Nested loops
 C programming allows to use one loop inside another
loop.
 Syntax for loop
for ( init; condition; increment ) {
for ( init; condition; increment ) {
statement(s);
}
statement(s);
}

2.4 Nested loops (Con)
 Syntax while loop
while(condition) {
while(condition) {
statement(s);
}
statement(s);
}

2.4 Nested loops (Con)
 Syntax do while loop
do {
statement(s);
do {
statement(s);
}while( condition );
}while( condition );

Example of Nested Loops
#include <stdio.h>
int main()
{
int n, c, k;
printf("Enter number of rowsn");
scanf("%d",&n);
for ( c = 1 ; c <= n ; c++ ){
for( k = 1 ; k <= c ; k++ )
printf("*");
printf("n");
}
return 0;
}

3. Break And Continue Statement
 What is BREAK meant?
 What is CONTINUE meant?

3.1 Break Statement
 The break statement terminates the loop immediately when
it is encountered.
 The break statement is used with decision making
statement such as if...else.
 Syntax of break statement
break;

Example: break statement
// Program to calculate the sum
of maximum of 10 numbers
// Calculates sum until user
enters positive number
# include <stdio.h>
int main() {
int i;
double number, sum = 0.0;
for(i=1; i <= 10; ++i) {
printf("Enter a n%d: ",i);
scanf("%lf",&number);
// If user enters negative
number, loop is terminated
if(number < 0.0) {
break;
}
// sum = sum + number;
sum += number;
}
return 0;
}

3.2 Continue Statement
 The continue statement skips some statements inside the loop.
 The continue statement is used with decision making statement
such as if...else.
 Syntax of continue Statement
continue;

Flowchart of Continue Statement

Example: continue statement
// Program to calculate sum of
maximum of 10 numbers
// Negative numbers are skipped
from calculation
# include <stdio.h>
int main(){
int i;
double number, sum = 0.0;
for(i=1; i <= 10; ++i) {
printf("Enter a n%d: ",i);
// If user enters negative
number, loop is terminated
if(number < 0.0) {
continue;
}
// sum = sum + number;
sum += number;
}
return 0;
}

4. Switch...Case Statement
 The if...else if…else statement allows you to execute a block code among
many alternatives. If you are checking on the value of a single variable in
if...else if…else statement, it is better to use switch statement.
 The switch statement is often faster than nested if...else (not always).
Also, the syntax of switch statement is cleaner and easy to understand.

Syntax of switch...case
switch (n){
case constant1:
// code to be executed if n is equal to constant1;
break;
case constant2:
// code to be executed if n is equal to constant2;
break;
.
.
.
default:
// code to be executed if n doesn't match any constant
}

Example: switch Statement
// Program to create a simple calculator
// Performs addition, subtraction, multiplication or division
depending the input from user
# include <stdio.h>
int main() {
char operator;
double firstNumber,secondNumber;
printf("Enter an operator (+, -, *,): ");
scanf("%c", &operator);
printf("Enter two operands: ");
scanf("%lf %lf",&firstNumber, &secondNumber);

switch(operator) {
case '+':
printf("%.1lf + %.1lf = %.1lf",firstNumber, secondNumber, firstNumber+secondNumber);
break;
case '-':
printf("%.1lf - %.1lf = %.1lf",firstNumber, secondNumber, firstNumber-secondNumber);
break;
case '*':
printf("%.1lf * %.1lf = %.1lf",firstNumber, secondNumber, firstNumber*secondNumber);
break;
case '/':
printf("%.1lf / %.1lf = %.1lf",firstNumber, secondNumber, firstNumber/firstNumber);
break;
// operator is doesn't match any case constant (+, -, *, /)
default:
printf("Error! operator is not correct");
}
return 0; }

5. goto Statement
 The goto statement is used to alter the normal sequence of a C
program.

Syntax of goto Statement
goto label;
... .. ...
... .. ...
... .. ...
label:
statement;

What is Label?
 The label is an identifier. When goto statement is encountered,
control of the program jumps to label: and starts executing the code.

Example: goto Statement
// Program to calculate the sum and average of maximum of 5
numbers
// If user enters negative number, the sum and average of
previously entered positive number is displayed
# include <stdio.h>
int main(){
const int maxInput = 5;
int i;
double number, average, sum=0.0;
for(i=1; i<=maxInput; ++i){
printf("%d. Enter a number: ", i);

// If user enters negative number, flow of program moves to label
jump
if(number < 0.0)
goto jump;
sum += number; // sum = sum+number;
}
jump:
average=sum/(i-1);
printf("Sum = %.2fn", sum);
printf("Average = %.2f", average);
return 0;
}
Example: goto Statement

C Programming: Control Structure

C Programming: Control Structure

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C Programming: Control Structure