Author: saqibkhan

The C compiler promotes certain data types to a higher rank for the sake of achieving consistency in the arithmetic operations of integers.

In addition to the standard int data type, the C language lets you work with its subtypes such as char, short int, long int, etc. Each of these data types occupy a different amount of memory space. For example, the size of a standard int is 4 bytes, whereas a char type is 2 bytes of length. When an arithmetic operation involves integer data types of unequal length, the compiler employs the policy of integer promotion.

Integer Promotions

As a general principle, the integer types smaller than int are promoted when an operation is performed on them. If all values of the original type can be represented as an int, the value of the smaller type is converted to an int; otherwise, it is converted to an unsigned int.

One must understand the concept of integer promotion to write reliable C code, and avoid unexpected problems related to the size of data types and arithmetic operations on smaller integer types.

Example

In this example, the two variables a and b seem to be storing the same value, but they are not equal.

#include <stdio.h>intmain(){char a =251;unsignedchar b = a;printf("a = %c", a);printf("\nb = %c", b);if(a == b)printf("\n Same");elseprintf("\n Not Same");return0;}

Output

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

a = 
b = 
Not Same

You get this output because “a” and “b” are treated as integers during comparison. “a” is a signed char converted to int as -5, while “b” is an unsigned char converted to int as 251.

Example: Mechanism of Integer Promotions

Let us try to understand the mechanism of integer promotions with this example −

#include <stdio.h>intmain(){char a ='e', b ='2', c ='M';char d =(a * b)/ c;printf("d as int: %d as char: %c", d, d);return0;}

Output

Run the code and check its output −

d as int: 65 as char: A

When Integer Promotion is Applied?

In the arithmetic expression “(a * b) / c”, the bracket is solved first. All the variables are of signed char type, which is of 2 byte length and can store integers between -128 to 127. Hence the multiplication goes beyond the range of char but the compiler doesn’t report any error.

The C compiler applies integer promotion when it deals with arithmetic operations involving small types like char. Before the multiplication of these char types, the compiler changes them to int type. So, in this case, (a * b) gets converted to int, which can accommodate the result of multiplication, i.e., 1200.

Example

Integer promotions are applied as part of the usual arithmetic conversions to certain argument expressions; operands of the unary +, -, and ~ operators; and operands of the shift operators. Take a look at the following example −

#include <stdio.h>intmain(){char a =10;int b = a >>3;printf("b as int: %d as char: %c", b, b);return0;}

Output

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

b as int: 1 as char: 

In the above example, shifting the bit structure of “a” to the left by three bits still results in its value within the range of char (a << 3 results in 80).

Example

In this example, the rank of the char variable is prompted to int so that its left shift operation goes beyond the range of char type.

#include <stdio.h>intmain(){char a =50;int b = a <<2;printf("b as int: %d as char: %c", b, b);return0;}

Output

Run the code and check its output −

b as int: 200 as char: 

Integer Promotion Rules

Promotion rules help the C compiler in maintaining consistency and avoiding unexpected results. The fundamental principle behind the rules of promotion is to ensure that the expression’s type is adjusted to accommodate the widest data type involved, preventing data loss or truncation.

Here is a summary of promotion rules as per C11 specifications −

• The integer types in C are char, short, int, long, long long and enum. Booleans are also treated as an integer type when it comes to type promotions.
• No two signed integer types shall have the same rank, even if they have the same representation.
• The rank of a signed integer type shall be greater than the rank of any signed integer type with less precision.
• The rank of long int > the rank of int > the rank of short int > the rank of signed char.
• The rank of char is equal to the rank of signed char and unsigned char.
• Whenever a small integer type is used in an expression, it is implicitly converted to int which is always signed.
• All small integer types, irrespective of sign, are implicitly converted to (signed) int when used in most expressions.

In short, we have the following integer promotion rules −

• Byte and short values − They are promoted to int.
• If one operand is a long − The entire expression is promoted to long.
• If one operand is a float − The entire expression is promoted to float.
• If any of the operands is double − The result is promoted to double.

Example

Here, the variables x and y are of char data type. When the division operation is performed on them, they automatically get promoted to int and the resultant value is stored in z.

#include <stdio.h> intmain(){char x =68;char y =34;printf("The value of x is: %d", x);printf("\nThe value of y is: %d", y);char z = x/y;printf("\nThe value of z: %d", z);return0;}

Output

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

The value of x is: 68
The value of y is: 34
The value of z: 2

Unlike the int, char or float types, the ANSI C standard doesnt have a built-in or primary Boolean type. A Boolean or bool data generally refers to the one that can hold one of the two binary values: true or false (or yes/no, on/off, etc.). Even if the bool type is not available in C, you can implement the behaviour of Booleans with the help of an enum type.

The new versions of C compilers, complying with the C99 standard or later, support the bool type, which has been defined in the header file stdbool.h.

Using enum to Implement Boolean Type in C

The enum type assigns user-defined identifiers to integral constants. We can define an enumerated type with true and false as the identifiers with the values 1 and 0.

Example

1 or any other number that is not 0 represents true, whereas 0 represents false.

#include <stdio.h>intmain(){enumbool{false, true};enumbool x = true;enumbool y = false;printf("%d\n", x);printf("%d\n", y);}

Output

Run the code and check its output −

1
0

typedef enum as BOOL

To make it more concise, we can use the typedef keyword to call enum bool by the name BOOL.

Example 1

Take a look at the following example −

#include <stdio.h>intmain(){typedefenum{false, true} BOOL;

   BOOL x = true;
   BOOL y  = false;printf("%d\n", x);printf("%d\n", y);}

Here too, you will get the same output −

Output

1
0

Example 2

We can even use the enumerated constants in the decision-making or loop statements −

#include <stdio.h>intmain(){typedefenum{false, true} BOOL;int i =0;while(true){
  i++;printf("%d\n", i);if(i &gt;=5)break;}return0;}</code></pre>


Output



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



1
2
3
4
5




Boolean Values with #define



The #define preprocessor directive is used to define constants. We can use this to define the Boolean constants, FALSE as 0 and TRUE as 1.



Example



Take a look at the following example −



#include <stdio.h>#define FALSE 0#define TRUE 1intmain(){printf("False: %d \n True: %d", FALSE, TRUE);return0;}



Output



Run the code and check its output −



False: 0 
 True: 1




Boolean Type in stdbool.h



The C99 standard of C has introduced the stdbool.h header file. It contains the definition of bool type, which actually is a typedef alias for _bool type. It also defines the macros true which expands to 1, and false which expands to 0.



Example 1



We can use the bool type as follows −



#include <stdio.h>#include <stdbool.h>intmain(){

   bool a = true;
   bool b = false;printf("True: %d\n", a);printf("False: %d", b);return0;}



Output



On executing this code, you will get the following output −



True: 1
False: 0




Example 2



We can use bool type variables in logical expressions too, as shown in the following example −



#include <stdio.h>#include <stdbool.h>intmain(){
  
   bool x;
   x =10>5;if(x)printf("x is True\n");elseprintf("x is False\n");
   bool y;int marks =40;
   y = marks >50;if(y)printf("Result: Pass\n");elseprintf("Result: Fail\n");}



Output



Run the code and check its output −



x is True
Result: Fail




Example 3



Let us implement a while loop with the help of a bool variable −



#include <stdio.h>#include <stdlib.h>#include <stdbool.h>intmain(void){

   bool loop = true;int i =0;while(loop){
  i++;printf("i: %d \n", i);if(i &gt;=5)
     loop = false;}printf("Loop stopped!\n");return EXIT_SUCCESS;}</code></pre>


Output



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



i: 1
i: 2
i: 3
i: 4
i: 5
Loop stopped!

Escape Sequence in C

An escape sequence in C is a literal made up of more than one character put inside single quotes. Normally, a character literal consists of only a single character inside single quotes. However, the escape sequence attaches a special meaning to the character that appears after a backslash character (\).

The \ symbol causes the compiler to escape out of the string and provide meaning attached to the character following it.

Look at \n as an example. When put inside a string, the \n acts as a newline character, generating the effect of pressing the Enter key. The following statement −

printf(" Hello \n World ");

Will produce this output −

Hello
World

The new line is an unprintable character. The \n escape sequence is useful to generate its effect. Similarly, the escape sequence \t is equivalent to pressing the Tab key on the keyboard.

An escape sequence is a sequence of characters that does not represent itself when used inside a character or string literal but is translated into another character or a sequence of characters that may be difficult or impossible to represent directly.

All Escape Sequences in C

In C, all escape sequences consist of two or more characters, the first of which is the backslash \ (called the “Escape character”); the remaining characters have an interpretation of the escape sequence as per the following table.

Here is a list of escape sequences available in C −

Escape sequence	Meaning
\\	\ character
\’	‘ character
\”	” character
\?	? character
\a	Alert or bell
\b	Backspace
\f	Form feed
\n	Newline
\r	Carriage return
\t	Horizontal tab
\v	Vertical tab
\ooo	Octal number of one to three digits
\xhh . . .	Hexadecimal number of one or more digits

Let us understand how these escape sequences work with the help of a set of examples.

Newline Escape Sequence (\n)

The newline character, represented by the escape sequence \n in C, is used to insert the effect of carriage return on the output screen. You would use this escape sequence to print text in separate lines and improve the readability of output.

Example

Take a look at the following example −

#include <stdio.h>intmain(){printf("Hello.\nGood morning.\nMy name is Ravi");}

Output

On running this code, you will get the following output −

Hello.
Good morning.
My name is Ravi

Tab Escape Sequence (\t)

The tab character (\t) represents the Tab key on the keyboard. When the tab character is encountered in a string, it causes the cursor to move to the next horizontal tab stop. Horizontal tab stops are usually set at intervals of eight characters.

Example

Take a look at the following example −

#include <stdio.h>intmain(){printf("Name:\tRavi\tMarks:\t50");}

Output

Run the code and check its output −

Name:   Ravi    Marks:  50

Backslash Escape Sequence (\\)

To add backslash character itself as a part of a string, it must precede by another backslash. First backslash escapes out of the string, and the second one takes the effect.

Example

Take a look at the following example −

#include <stdio.h>intmain(){printf("Directory in Windows: C:\\users\\user");}

Output

On running this code, you will get the following output −

Directory in Windows: C:\users\user

Double and Single Quotes Escape Sequences (\” and \’)

These characters have a special meaning in C since ” and ‘ symbols are used for the representation of a character literal and a string literal respectively. Hence, to treat these characters as a part of the string, they must be escaped with an additional backslash preceding them.

Example

Take a look at the following example −

#include <stdio.h>intmain(){printf("Welcome to \"TutorialsPoint\"\n");printf("\'Welcome\' to TutorialsPoint");}

Output

Run the code and check its output −

Welcome to "TutorialsPoint"
'Welcome' to TutorialsPoint

Backspace Escape Sequence (\b)

The escape sequence “\b”, represents the backspace character. It is used erase a character or a specific portion of a text that has already been printed on the screen.

Example

Check the following example code −

#include <stdio.h>intmain(){printf("Welcome to\b TutorialsPoint");}

Output

Run the code and check its output −

Welcome t TutorialsPoint

Note that o from to has been erased.

C also has a \r escape sequence. The newline escape sequence (\n) moves the cursor to the beginning of the next line, while the carriage return escape sequence (\r) moves the cursor to the beginning of the current line.

Octal Number Escape Sequence (\ooo)

This escape sequence is used for Octal numbers of one to three digits. An octal escape sequence is a backslash followed by one, two, or three octal digits (0-7). It matches a character in the target sequence with the value specified by those digits.

Example

Take a look at the following example −

#include <stdio.h>intmain(){printf("%c",'\141');return0;}

Output

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

a

Hexadecimal Number Escape Sequence (\xhh)

A hexadecimal escape sequence is a backslash followed by the letter “x” followed by two hexadecimal digits (0-9a-fA-F). It matches a character in the target sequence with the value specified by the two digits.

Example

Take a look at the following example −

#include <stdio.h>intmain(){printf("%c",'\x41');return0;}

Output

Here, you will get the following output −

A

Alert or Bell Number Escape Sequence (\a)

The escape sequence \a represents the alert or bell character. When executed, it produces a sound or visual alert depending on the terminal or console being used.

Example

Take a look at the following example −

#include <stdio.h>intmain(){printf("Hello \a world\n");return0;}

Output

Run the code and check its output −

Hello  world

Escape sequences are used widely in many other programming languages such as Java, PHP, C#, etc.