The statements which alter flow of execution of a program are known as control statements.
There are two types of control statements: Decision Making & Repeating construct
Decision Making Statements Loop Statements or Repeating construct
if statements for loop
if.. else statements while loop
if.. else if statements do.. while loop
Nested if.. else statement
switch statement
Decision Making Statements
i. if Statements
An if statements is used to control the flow of execution of statements. The if statement first evaluates an expression and then, it executes the statements within its block if the value of the evaluated expression is true.
if(test_ expression)
{
statements-block;
}
Example 1
Write a program to read a number from user and test whether the number is negative [Show message “The number is negative ” if it is negative number otherwise show nothing].
#include<stdio.h>
#include<conio.h>
int main()
{
int num;
printf("Enter a number to be tested:");
scanf("%d", &num);
if(num<0)
printf("The number is negative");
getch();
return 0;
}
Output
Enter a number to be tested:-6
The number is negative
Nested if Statement
When one if statement is written within body of another if statement, it is called nested if statement if statement. The several if statements shall be declared as nested if statements.
Syntax
if(expression)
{
if(expression)
{
//body
}
}
Example
Write a program to read percentage of marks obtained by a student in SLC and +2 level, Display message “Congratulation!! You have first division in both SLC and +2” if both levels have percentage greater than or equal to 60.
#include<Stdio.h>
#include<conio.h>
int main()
{
float SLC_ per, plus2_ per; ;
print f("Enter percentage of SLC:");
scan f("%f", &SLC_ per)
print f("Enter percentage in +2 in science:");
scan f("%f", &plus2_per);
if(SLC_ per>=60)
{
if(plus2_per>=60)
{
print f("Congratulation!!");
print f("\n You have first division in both SLC and +2.");
}
}
getch () ;
return 0;
}
Output
Enter percentage of SLC: 70
Enter percentage in +2 in science: 60
Congratulation!!!!!
You have first division in both SLC and +2.
if…. else Statement
The if.. else statement is an extension of the simple if statement . It is used when there are only two possible actions one happens when a test condition is true, and the other when it is false.
if(test_ expression)
{
true-block statement (s);
}
else
{
false-block statement (s);
}
Example
Write a program to read a number from user and determine whether the number is even or odd.
#include<stdio.h>
#include<conio.h>
int main()
{
int num, remainder;
print f("Enter a number:");
scan f("%d", &num);
remainder = num % 2;
// Modulo division
if (remainder == 0)
{
print f("The number is even");
}
else
{
print f("The number is odd");
}
getch();
return 0;
}
Output
Enter a number : 90
The number is : even
Enter a number: 17
The number is odd
Similar to nested if statement if.. else statements shall also be written inside the body of another if.. else body called nested if.. else statement.
if(condition)
{
if(condition2)
{
statement-1;
}
else
{
statement-2;
}
}
else
{
if(condition3)
{
statement-3;
}
else
{
statement-4;
}
}
Example
Write a program to read three number from user and determine the largest number among them.
int main()
int n1, n2, n3;
print f("Enter 3 numbers:");
scan f ("%d%d%d", &n1 , &n2 , &n3);
if (n1>n2)
{
if(n1>n3)
print f("Largest = %d , n1);
else
print f("Largest = %d", n3);
}
else
{
if (n2>n3)
print f("Largest = %d , n2);
else
print f("Largest = %d, n3);
}
getch();
return 0;
}
Output
Enter 3 number : 100 50 10
Largest = 100
Enter 3 number : 50 100 10100
Largest = 100
An if… else if statement is used when there are more than two possible actions depending upon the outcome of test expression. When an action is taken, no others can be executed or taken. In such situation, if…. else if… else if.. else structure is used.
if(condition)
{
statement-1;
}
else if(condition2)
{
statement-2;
}
else if(condition3)
{
statement-3;
}
else if(condition n)
{
statement-n;
}
else
{
default-statement;
}
statement-x;
Example
Write a program that reads total marks of a student in seven subjects. Then calculate the percentage and determine the division. Use following conditions:
- Percentage greater than or equal to 80- distinction,
- Percentage between 60 and 79- First Division
- Percentage between 45 and 59-second division
- Percentage between 32 and 44 – third division
- Percentage less than or equal to 31 -fail.
#include<stdio.h>
#include<conio.h>
int main()
{
float nep, eng, math, phy, chem, bio, comp, percent;
print f("Enter the marks in 7 subjects:");
scan f("%f%f%f%f%f%f%f", &nep, &eng, &math, &phy, &chem, &bio, &comp);
percent =(nep+ eng + math +phy + chem + bio + comp) ;
if(percent>= 80)
print f("Distinction");
else if(percent >=60 && percent < 80)
print f ("First Division");
else if (percent>=45 && percent <60)
print f("Second Division")
else if (percent >=32 && percent <45)
print f("Third Division");
else
print f("Fail");
print f("\n Your percentage is: %f", percent);
getch();
return 0;
}
Output:
i. Enter the marks in 7 subjects: 45 78 89 35 76 80 35
First Division
Your percentage is :62.5714286
ii. Enter the marks in 7 subjects: 20 10 32 25 24 35 40
Fail
Your percentage is: 26.5714286
Types of Loop
- for loop
- while loop
- do-while loop
i. for Loop
for(counter_ initialization; test_ condition; increment or decrement)
{
statements; or body of loop
}
Example
Write a program to calculate factorial of a number.
#include<stdio.h>
#include<conio.h>
int main()
{
int num, i;
long fact=1;
print f("\n Enter a number whose factorial is to be calculated:");
scan f("%d", &num);
for(i=1;i<=num;i++)
fact*= i;
print f("\n The factorial is :%d", fact);
getch();
return 0;
}
Output
Enter a number whose factorial is to be calculated : 5
The factorial is : 120
While(test_ condition)
{
body of loop
}
Example
Write a program to calculate factorial of a number using while loop.
#include<stdio.h>
#include<conio.h>
int main()
{
int num, i=1;
long fact = 1;
print f("Enter a number whose factorial is to be calculated:");
scan f("%d", &num);
while(i<=num)
{
fact*=i;
i++;
}
print f("The factorial is:%d", fact);
getch();
return 0;
}
Do
{
//statements or body of loop;
}while(test_condition);
Example
Write a program to read a number from keyword until a zero or a negative number is keyed in. Finally, calculate sum and average of entered numbers.
#include<stdio.h>
#include<conio.h>
int main()
{
int num, count=0;
float sum=0, avg;
do
{
print f("\n Enter number:\t");
scan f("%d", &num);
sum+=num;
count++;
}while(num>0);
sum=sum-num;
avg=(sum)/(count-1)
print f("\n The sum is :\t%d", sum);
print f("\n The average is: \t%f", avg);
getch();
return 0;
}
Output
Enter number: 10
Enter number: 20
Enter number: 15
Enter number: 5
Enter number: 0
The sum is: 50.000000
The average is: 12.500000
break Statement
The break statement terminates the execution of the loop and the control is transferred to the statement immediately following the loop.
break;
Example
What is the output of following program?
#include<stdio.h>
#include<conio.h>
int main()
{
int i;
for(i=1; i<10; i++)
{
print f("\t%d, i);
if (i==5)
break;
}
getch();
}
Output
1 2 3 4 5
continue Statement
The continue statement is used when we want to continue running the loop.
continue;
Example
Write a program that asks for a number n from user and then display only even numbers from 2 to n .
#include<stdio.h>
#include<conio.h>
int main()
{
int i, num;
print f("\n Enter a number:");
scan f("%d", &num);
print f("\n The even numbers from 2 to %d are: \n", num);
for (i=1; i<= num; i++)
{
if(i%2!=0)
continue;
print f("\t%d", i);
}
getch();
return 0;
}
Output
Enter a number: 20
The even numbers from 2 to 20 are:
2 4 6 8 10 12 14 16 18 20
goto STATEMENT
The goto statement is used to after the normal sequence of program execution by unconditionally transferring control to some part of the program.
goto label; label: statements;
Example
Write a program to ask two numbers. Display message” Either number is negative ” if either number is negative ; otherwise display message ” Both numbers are positive”.
int main()
{
int i, num1, num2;
print f("Enter first number:");
scan f("%d", &num1);
if(num<0)
goto negative;
print f("Enter second number:");
scan f("%d", &num2);
if(num2<0)
goto negative;
print f("The both numbers are positive");
getch();
return;
negative :
print f("Enter number is negative ");
getch();
return 0;
}
Output
a) Enter first number: 20
Enter second number: 10
The both numbers are positive
b) Enter first number: -5
Either number is negative
c) Enter first number : 6
Enter second number: -4
Either number is negative
When there are a number of options available and one of them is to be selected on the basis of some criteria, switch statement is used.
switch(variable or expression)
{
case caseConstant1:
statements;
break;
case caseConstant2:
statements;
break;
default:
statements;
}