IF Sample Program 1

Now let’s see the usage of relational operators by an example. There are two students Amer and Amara. We take their ages from the user, compare them and tell who is older?
As there are two students to be compared in terms of age, we need to declare two variables to store their ages. We declare two variables AmerAge and AmaraAge of type int. The variable names are one continuous word as we can’t use spaces in a variable name.
Here is an important point about variables declaration. We should assign an initial value (preferably 0 for integers) to variables when we declare them. This is called initialization of variables.
We can do this in one line while declaring a variable like int x = 0; This statement will declare a variable of name x with data type int and will assign a value 0 to this variable. Initializing a variable in this way is just a matter of style. You can initialize a variable on a separate line after declaring it. It is a good programming practice to initialize a variable.
Now we prompt the user to enter Amer’s age and store it into variable AmerAge. Then similarly we get Amara’s age from the user in the variable AmaraAge.
While comparing the ages, we will use the if statement to see whether Amer’s age is greater than Amara’s. We will use > (greater than) operator to compare the ages. This can be written as if ( AmerAge > AmaraAge) .
With this if statement, we write the statement cout << "Amer is greater than Amara" ; It’s a simple one line test i.e. ‘if Amer’s age is greater than Amara's’, then display the message ‘Amer is older than Amara’. Flow chart of the sample program:


The complete code of the program is given below.



In our program, we write a single statement with the if condition. This statement executes if the condition is true. If we want to execute more than one statements, then we have to enclose all these statements in curly brackets { }. This comprises a block of statements which will execute depending upon the condition. This block may contain a single statement just like in our problem. So we can write the if statement as follow.



A sample execution of the program results the following output.



Now think what happens if the condition in the if statement is not true i.e. Amer’s age is not greater than Amara’s. In this case, if the user enters Amer’s age less than Amara’s, then our program does nothing. So to check this condition, another if statement after the first if statement is required. Then our program will be as:



Now our program decides properly about the ages entered by the user.
After getting ages from the user, the if statements are tested and if statement will be executed if the condition evaluates to true.

For previous lesson click here: Flow Charting
For next lesson click here: If/else Structure

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IF Sample Program 1

Conditional Statements

In every day life, we are often making decisions. We perform different tasks while taking decisions. For example, the statement ‘Bring one litre of milk while returning home from college, if the milk shop is open’ involves this phenomenon.
In this statement, there is an element of decision making. We bring one litre of milk if the shop is open. And if the shop is closed, we come back to home without milk.
Thus we are making a decision on the condition that the shop is open. The decision-making process is everywhere in our daily life. We see that the college gives admission to a student if he has the required percentage in his previous examination and/or in the entry test. Similarly administration of a basketball team of the college decides that the students having height more than six feet can be members of the team.
For writing interesting and useful programs, we have to develop the decision making power in them.
Now we will see what kind of decisions are in programming and how these can be used.

Every programming language provides a structure for decision making.
'C' also provides this structure. The statement used for decisions in 'C' language is known as the 'if statement'. The if statement has a simple structure. That is



We explain it as if condition is true, then execute the statement or a group of statements. Here the condition is a statement which explains the condition on which a decision will be made. We can understand it from the example that Ali can become the member of the basket ball team if he has a height more than six feet .In this case, the condition will be



We have written the condition in English language. Now let's see how we can implement this in terms of variables, operators and C statements. In the program, we will write the condition in parentheses, followed by a statement or group of statements to be executed.
Now here is the concept of block of statements. We use braces { } to make a group (block) of a number of statements. We put ‘{’ before first statement and ‘}’ after the last statement. Thus if we have to do many things after the if statement. The structure of if statement becomes as under



Note the indentation of the lines and semi-colon after each statement. Semi-colons are necessary after every C statement. The indentation is only a matter of style. It makes the code easy to read and understand from where a block starts, ends and what kind of block it is. It does not affect the logic of the program. But the braces can affect the logic. We can also write a comment line to state the purpose of code block.
Let's consider a simple example to explain the if statement. Suppose, we have ages of two students (say for the time being we have got these ages in variables). These variables are- age1 and age2. Now we say that if the age1 is greater than age2, then display the statement ‘Student 1 is older than student 2’.
The coding for this program will be as below



Here, in our code we see a new operator i.e. ‘ > ‘ (greater than) in the if statement. We need such operators (like greater than, less than, equal to etc) while making decisions. These operators are called 'relational operators'. These are almost the same relational operators we use in algebra.
Following table summarizes the relational operators.

	Algebraic	In C language	Example	Meaning
Greater than	>	>	x > y	x is greater than y
Equal to	=	==	x == y	X is equal to y
Less than	<	<	x < y	X is less than y
Greater than or equal to	≥	>=	x >= y	x is greater than or equal to y
Less than or equal to	≤	<=	x <= y	x is less than or equal to y
Not equal to	≠	!=	x != y	x is not equal to y

Note that there is no space between ==, >=, <= and !=. These are considered as single operators. The operator == (equal to) is different from the operator =. We know that operator = is the assignment operator which is used in assignment statement to assign a value to a variable. Don't confuse the assignment operator (=) with equal to operator (==). If we write single = in condition of if statement. For example, if we write if ( x = 2 ), the compiler will not give error. This means that it is not a syntax error. The conditional expression in if statement returns a value. In this case, x = 2 will also have some value but it will not in the form of true or false. So it will create a logical error. So be careful while using equal to condition in if statement. For previous lesson click here: Use of Operators
For next lesson click here: Flow Charting

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Conditional Statements