Assignment Operators in C: Assigning Values to Variables

Learn about the different assignment operators in C, which are used to store values in variables. Understand the basic assignment operator = and the compound assignment operators, such as +=, -=, *=, /= and %= for performing arithmetic operations and assignments in a concise manner. This guide will equip you with the knowledge to effectively assign values to variables in your C programs.

Assignment Operators in C

In C language, the assignment operator stores a certain value in an already declared variable. A variable in C can be assigned the value in the form of a literal, another variable, or an expression.

The value to be assigned forms the right-hand operand, whereas the variable to be assigned should be the operand to the left of the "=" symbol, which is defined as a simple assignment operator in C.

Assignment Operators

The following table lists the assignment operators supported by the C language:

Simple Assignment Operator (=)

The = operator is one of the most frequently used operators in C. As per the ANSI C standard, all the variables must be declared at the beginning. Variable declaration after the first processing statement is not allowed.

You can declare a variable to be assigned a value later in the code, or you can initialize it at the time of declaration. You can use a literal, another variable, or an expression in the assignment statement.

int x = 10; // declaration with initialization
int y;      // declaration
y = 20;     // assignment later
int z = x + y; // assign an expression
int d = 3, f = 5; // definition and initializing d and f
char x = 'x'; // the variable x has the value 'x'

Once a variable of a certain type is declared, it cannot be assigned a value of any other type. In such a case, the C compiler reports a type mismatch error.

In C, the expressions that refer to a memory location are called "lvalue" expressions. A lvalue may appear as either the left-hand or right-hand side of an assignment.

On the other hand, the term rvalue refers to a data value that is stored at some address in memory. An rvalue is an expression that cannot have a value assigned to it, which means an rvalue may appear on the right-hand side but not on the left-hand side of an assignment.

Variables are lvalues and so they may appear on the left-hand side of an assignment. Numeric literals are rvalues and so they may not be assigned and cannot appear on the left-hand side. Take a look at the following valid and invalid statements:

int g = 20; // valid statement
10 = 20;    // invalid statement

Augmented Assignment Operators

In addition to the = operator, C allows you to combine arithmetic and bitwise operators with the = symbol to form augmented or compound assignment operators. The augmented operators offer a convenient shortcut for combining arithmetic or bitwise operations with assignment.

Example 1

The expression a += b has the same effect as performing a + b first and then assigning the result back to the variable a.

#include <stdio.h>

int main(){
   int a = 10;
   int b = 20;
   
   a += b;
   printf("a: %d", a);
   
   return 0;
}

Output

a: 30

Example 2

The expression a <<= b has the same effect as performing a << b first and then assigning the result back to the variable a.

#include <stdio.h>

int main(){
   int a = 60;
   int b = 2;
   
   a <<= b;
   printf("a: %d", a);
   
   return 0;
}

Output

a: 240

Example 3

Here is a C program that demonstrates the use of assignment operators in C:

#include <stdio.h>

int main(){
   int a = 21;
   int c ;

   c =  a;
   printf("Line 1 - =  Operator Example, Value of c = %d\n", c );

   c +=  a;
   printf("Line 2 - += Operator Example, Value of c = %d\n", c );

   c -=  a;
   printf("Line 3 - -= Operator Example, Value of c = %d\n", c );

   c *=  a;
   printf("Line 4 - *= Operator Example, Value of c = %d\n", c );

   c /=  a;
   printf("Line 5 - /= Operator Example, Value of c = %d\n", c );

   c  = 200;
   c %=  a;
   printf("Line 6 - %%= Operator Example, Value of c = %d\n", c );

   c <<=  2;
   printf("Line 7 - <<= Operator Example, Value of c = %d\n", c );

   c >>=  2;
   printf("Line 8 - >>= Operator Example, Value of c = %d\n", c );

   c &=  2;
   printf("Line 9 - &= Operator Example, Value of c = %d\n", c );

   c ^=  2;
   printf("Line 10 - ^= Operator Example, Value of c = %d\n", c );

   c |=  2;
   printf("Line 11 - |= Operator Example, Value of c = %d\n", c );
   
   return 0;
}

Output

Line 1 - =  Operator Example, Value of c = 21
Line 2 - += Operator Example, Value of c = 42
Line 3 - -= Operator Example, Value of c = 21
Line 4 - *= Operator Example, Value of c = 441
Line 5 - /= Operator Example, Value of c = 21
Line 6 - %= Operator Example, Value of c = 11
Line 7 - <<= Operator Example, Value of c = 44
Line 8 - >>= Operator Example, Value of c = 11
Line 9 - &= Operator Example, Value of c = 2
Line 10 - ^= Operator Example, Value of c = 0
Line 11 - |= Operator Example, Value of c = 2