C Operators & If ... Else | C Programming for Beginners - Class 6 PDF Download

Operators

• Operators are used to perform operations on variables and values.
• In the example below, we use the + operator to add together two values:

Example

int myNum = 100 + 50;

Although the + operator is often used to add together two values, like in the example above, it can also be used to add together a variable and a value, or a variable and another variable:

Example

int sum1 = 100 + 50;        // 150 (100 + 50)

int sum2 = sum1 + 250;      // 400 (150 + 250)

int sum3 = sum2 + sum2;     // 800 (400 + 400)

C divides the operators into the following groups:

• Arithmetic operators
• Assignment operators
• Comparison operators
• Logical operators
• Bitwise operators

Arithmetic Operators

Arithmetic operators are used to perform common mathematical operations.

Assignment Operators

Assignment operators are used to assign values to variables.
In the example below, we use the assignment operator (=) to assign the value 10 to a variable called x:
Example

int x = 10;

The addition assignment operator (+=) adds a value to a variable:
Example

int x = 10;

x += 5;

Comparison Operators

Comparison operators are used to compare two values.
Note: The return value of a comparison is either true (1) or false (0).
In the following example, we use the greater than operator (>) to find out if 5 is greater than 3:

Example

int x = 5;

int y = 3;

printf("%d", x > y); // returns 1 (true) because 5 is greater than 3

Sizeof Operator

The memory size (in bytes) of a data type or a variable can be found with the sizeof operator:

Example

int myInt;

float myFloat;

double myDouble;

char myChar;

printf("%lu\n", sizeof(myInt));

printf("%lu\n", sizeof(myFloat));

printf("%lu\n", sizeof(myDouble));

printf("%lu\n", sizeof(myChar));

Note that we use the %lu format specifer to print the result, instead of %d. It is because the compiler expects the sizeof operator to return a long unsigned int (%lu), instead of int (%d). On some computers it might work with %d, but it is safer to use %lu.

C If ... Else

Conditions and If Statements

You learned from the operators comparison chapter, that C supports the usual logical conditions from mathematics:

• Less than: a < b
• Less than or equal to: a <= b
• Greater than: a > b
• Greater than or equal to: a >= b
• Equal to a == b
• Not Equal to: a != b

You can use these conditions to perform different actions for different decisions.

C has the following conditional statements:

• Use if to specify a block of code to be executed, if a specified condition is true
• Use else to specify a block of code to be executed, if the same condition is false
• Use else if to specify a new condition to test, if the first condition is false
• Use switch to specify many alternative blocks of code to be executed

The if Statement

Use the if statement to specify a block of C code to be executed if a condition is true.

Syntax

if (condition) {

  // block of code to be executed if the condition is true

}

Note that if is in lowercase letters. Uppercase letters (If or IF) will generate an error.

In the example below, we test two values to find out if 20 is greater than 18. If the condition is true, print some text:
Example

if (20 > 18) {

  printf("20 is greater than 18");

}

We can also test variables:

Example

int x = 20;

int y = 18;

if (x > y) {

  printf("x is greater than y");

}

Example explained

In the example above we use two variables, x and y, to test whether x is greater than y (using the > operator). As x is 20, and y is 18, and we know that 20 is greater than 18, we print to the screen that "x is greater than y".

The else Statement

Use the else statement to specify a block of code to be executed if the condition is false.

Syntax

if (condition) {

  // block of code to be executed if the condition is true

} else {

  // block of code to be executed if the condition is false

}

Example

int time = 20;

if (time < 18) {

  printf("Good day.");

} else {

  printf("Good evening.");

}

// Outputs "Good evening."

Example explained

In the example above, time (20) is greater than 18, so the condition is false. Because of this, we move on to the else condition and print to the screen "Good evening". If the time was less than 18, the program would print "Good day".

The else if Statement

Use the else if statement to specify a new condition if the first condition is false.

Syntax

if (condition1) {

  // block of code to be executed if condition1 is true

} else if (condition2) {

  // block of code to be executed if the condition1 is false and condition2 is true

} else {

  // block of code to be executed if the condition1 is false and condition2 is false

}

Example

int time = 22;

if (time < 10) {

  printf("Good morning.");

} else if (time < 20) {

  printf("Good day.");

} else {

  printf("Good evening.");

}

// Outputs "Good evening."

Example explained

In the example above, time (22) is greater than 10, so the first condition is false. The next condition, in the else if statement, is also false, so we move on to the else condition since condition1 and condition2 is both false - and print to the screen "Good evening".
However, if the time was 14, our program would print "Good day."

Another Example

This example shows how you can use if..else if to find out if a number is positive or negative:

Example

int myNum = 10; // Is this a positive or negative number?

if (myNum > 0)

  printf("The value is a positive number.");

else if (myNum < 0)

  printf("The value is a negative number.");

else

  printf("The value is 0.");

Short Hand If...Else (Ternary Operator)

variable = (condition) ? expressionTrue : expressionFalse;

Instead of writing:

Example

int time = 20;

if (time < 18) {

  printf("Good day.");

} else {

  printf("Good evening.");

}

You can simply write:

Example

int time = 20;

(time < 18) ? printf("Good day.") : printf("Good evening.");

It is completely up to you if you want to use the traditional if...else statement or the ternary operator.