Lecture 8 – Decisions (if)

Decisions (if)

There are situations when we need to take a decision. For example you are going to your home and there’s a traffic jam, you opt for alternate route. Similarly in C programming there are situations where we need to change the course of our program flow based upon a condition.

There are some decision constructs in C which help us to achieve that functionality.

if structure


It is used when you need to take a decision. Its general syntax is

Syntax


if (condition)

{

// Statements to be executed when the condition is true

}

Let’s understand it using an example

// This program demonstrates the use of if




Output

Please enter your marks: 75

Congratulations! You’ve passed
# include <stdio.h>




# include <conio.h>




Output

Please enter your marks: 25

 

void main()

{




Output

Please enter your marks: 50

 

int marks;

clrscr();                                                                                                




In last two examples there was no output because, those conditions were not handled in this code

printf(“\nPlease enter your marks: ”);

scanf(“%d”, &marks);

if(marks>50)

{

printf(“\nCongratulations! You’ve passed”);

}

getch();

}

Example 15 – Use of if and a relational operator

 

 




Output

Please enter your marks: 75

Congratulations! You’ve passed

// This program demonstrates the use of multiple if’s

# include <stdio.h>

# include <conio.h>

void main()




Output

Please enter your marks: 25

Sorry! You didn’t make it :(

{

int marks;

clrscr();                                                                                                




Output

Please enter your marks: 50

Sorry! You didn’t make it :(

 

printf(“\nPlease enter your marks: ”);

scanf(“%d”, &marks);

if(marks>50)




In last example the output is not what is expected. This is called a logical error. This condition is not handled in this code.

{

printf(“\nCongratulations! You’ve passed”);

}

If(marks < 50)

{

printf(“\nSorry! You didn’t make it :(”);

}

getch();

}

Example 16 – Use of multiple if's and two relational operators

// This program demonstrates the use of multiple if’s

# include <stdio.h>

# include <conio.h>




Output

Please enter your marks: 75

Congratulations! You’ve passed




Output

Please enter your marks: 25

Sorry! You didn’t make it :(




Output

Please enter your marks: 50

Congratulations! You’ve passed

 

void main()

{

int marks;

clrscr();                                                                                                

printf(“\nPlease enter your marks: ”);

scanf(“%d”, &marks);

if(marks>=50)

{

printf(“\nCongratulations! You’ve passed”);

}

If(marks < 50)

{

printf(“\nSorry! You didn’t make it :(”);

}

getch();

}

Example 17 – Use of multiple if's and different relational operators

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