Expressions in C

Arithmetic Expressions in C

These expressions perform arithmetic operations on both literals and variables. Some of the commonly used arithmetic operators are + (addition), – (subtraction), * (multiplication), / (division) and % (modulus). For example, the expression 5+6 will add 5 and 6 to give the result 11.

Arithmetic expressions can also make use of assignment operator (=) to assign a value to a variable. For example, the expression c=5+6 will assign the value 11 to the variable c.

#include <stdio.h>
int main()
{
    int a = 5, b = 6, c;
    c = a + b;
    printf("%d", c);
}

Output:
11

Relational Expressions in C

These expressions compare two values or variables and return either true or false based on the outcome of the comparison. The commonly used relational operators are == (equal to), != (not equal to), > (greater than), < (less than), >= (greater than or equal to) and <= (less than or equal to).

For example, the expression 5>6 will return false as 5 is not greater than 6 while the expression 6>=6 will return true as 6 is greater than or equal to 6.

#include <stdio.h>
int main()
{
    int a = 5, b = 6;
    if(a>b)
    {
        printf("true");
    }printf("false");
}

Output:
false

Logical Expressions in C

These expressions are used to test certain conditions and produce boolean outputs (true or false). Logical expressions are often used in control flow statements such as if-else and switch-case to execute a certain block of code only if a particular condition is satisfied.

Example:

#include <stdio.h>
int main()
{
    int i = 1;
    if (i++ && (i == 1))
        printf("Yes\n");
    else
        printf("No\n");
}

Output:
No

Conditional Expressions in C

The conditional expression is a operator that takes three operands. The first operand is a boolean expression, and the second and third operands are values. Conditional operator, also known as the ternary operator.

Syntax:

expression1 ? expression2 : expression3;

Example:

#include <stdio.h>
void main()
{
    int a = 8;
    int b = 7;
    int c = a < b ? a = b : b++;
    printf("%d", c);
}

Output:
7

Operator Precedence

Every C expression has a Numeric value. There are certain Rules regarding the evaluation of expressions. The Operator Precedence & its Associativity determine in which order & which operators to be evaluated first, next and so on in a given expression. For example:

    x = 20;
    /* assignment operator '=' assigns value to right of this to the */
    /* variable left of this. result of exp x = 20; is 20 */
 
    y = 20; 
    z = x + y;  /* z gets value 40 */
    x + y;      /* this expression results 40 */
    x > y;      /* relational expression results 0 here */

Relational Expressions, Logical Expressions have values either True or False that is 1 or 0. C99 standard provides a new type _Bool which allows only two values 0 & 1 for false & true.

A C program comprises of Statements each of which, mostly, in turn comprises of expressions. For example:

In the above program, we used return value of scanf() fun to terminate the loop. When we enter q to quit, scanf() failed to read & returns 0 and therefore loop terminates.

A C expression may also contain sub expression. For example:

    x + y * (a = b / c);    /* (a = b / c) is a sub-exp */ 
 
/* In the above exp., sub-exp is evaluated first because parentheses have */
/* higher precedence. */
/* The result of sub-exp is value of the variable to the left side of the */
/* assignment operator.*/
/* result is then multiplied to the value of y. Then the product is added */
/* to x */

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