Relational Operators in C

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Relational operators in C are defined to perform comparison of two values. The familiar angular brackets < and > are the relational operators in addition to a few more as listed in the table below.

These relational operators are used in Boolean expressions. All the relational operators evaluate to either True or False.

C doesnt have a Boolean data type. Instead, "0" is interpreted as False and any non-zero value is treated as True.

Example 1

Here is a simple example of relational operator in C −

 #include <stdio.h> int main(){ int op1 = 5; int op2 = 3; printf("op1: %d op2: %d op1 < op2: %d\n", op1, op2, op1 < op2); return 0; }

Output

Run the code and check its output −

 op1: 5 op2: 3 op1 < op2: 0

Relational operators have an important role to play in decision-control and looping statements in C.

The following table lists all the relational operators in C −

Operator Description Example
== Checks if the values of two operands are equal or not. If yes, then the condition becomes true. (A == B)
!= Checks if the values of two operands are equal or not. If the values are not equal, then the condition becomes true. (A != B)
> Checks if the value of left operand is greater than the value of right operand. If yes, then the condition becomes true. (A > B)
< Checks if the value of left operand is less than the value of right operand. If yes, then the condition becomes true. (A < B)
>= Checks if the value of left operand is greater than or equal to the value of right operand. If yes, then the condition becomes true. (A >= B)
<= Checks if the value of left operand is less than or equal to the value of right operand. If yes, then the condition becomes true. (A <= B)

All the relational operators are binary operators. Since they perform comparison, they need two operands on either side.

We use the = symbol in C as the assignment operator. So, C uses the "==" (double equal) as the equality operator.

The angular brackets > and < are used as the "greater than" and "less than" operators. When combined with the "=" symbol, they form the ">=" operator for "greater than or equal" and "<=" operator for "less than or equal" comparison.

Finally, the "=" symbol prefixed with "!" (!=) is used as the inequality operator.

Example 2

The following example shows all the relational operators in use.

 #include <stdio.h> int main(){ int a = 21; int b = 10; int c ; printf("a: %d b: %d\n", a,b); if(a == b){ printf("Line 1 - a is equal to b\n" ); } else { printf("Line 1 - a is not equal to b\n" ); } if (a < b){ printf("Line 2 - a is less than b\n" ); } else { printf("Line 2 - a is not less than b\n" ); } if (a > b){ printf("Line 3 - a is greater than b\n" ); } else { printf("Line 3 - a is not greater than b \n\n" ); } /* Lets change value of a and b */ a = 5; b = 20; printf("a: %d b: %d\n", a,b); if (a <= b){ printf("Line 4 - a is either less than or equal to b\n" ); } if (b >= a){ printf("Line 5 - b is either greater than or equal to b\n" ); } if(a != b){ printf("Line 6 - a is not equal to b\n" ); } else { printf("Line 6 - a is equal to b\n" ); } return 0; }

Output

When you run this code, it will produce the following output −

 a: 21 b: 10 Line 1 - a is not equal to b Line 2 - a is not less than b Line 3 - a is greater than b a: 5 b: 20 Line 4 - a is either less than or equal to b Line 5 - b is either greater than or equal to b Line 6 - a is not equal to b

Example 3

The == operator needs to be used with care. Remember that "=" is the assignment operator in C. If used by mistake in place of the equality operator, you get an incorrect output as follows −

 #include <stdio.h> int main(){ int a = 5; int b = 3; if (a = b){ printf("a is equal to b"); } else { printf("a is not equal to b"); } return 0; }

Output

The value of "b" is assigned to "a" which is non-zero, and hence the if expression returns true.

 a is equal to b

Example 4

We can have "char" types too as the operand for all the relational operators, as the "char" type is a subset of "int" type. Take a look at this example −

 #include <stdio.h> int main(){ char a = 'B'; char b = 'd'; printf("a: %c b: %c\n", a,b); if(a == b){ printf("Line 1 - a is equal to b \n"); } else { printf("Line 1 - a is not equal to b \n"); } if (a < b){ printf("Line 2 - a is less than b \n"); } else { printf("Line 2 - a is not less than b \n"); } if (a > b) { printf("Line 3 - a is greater than b \n"); } else { printf("Line 3 - a is not greater than b \n"); } if(a != b) { printf("Line 4 - a is not equal to b \n"); } else { printf("Line 4 - a is equal to b \n"); } return 0; }

Output

Run the code and check its output −

 a: B b: d Line 1 - a is not equal to b Line 2 - a is less than b Line 3 - a is not greater than b Line 4 - a is not equal to b

Relational operators cannot be used for comparing secondary types such as arrays or derived types such as struct or union types.

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