QBASIC Functions: Understanding Library Functions, LEFT$, MID etc.

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A function is a built-in formula to accomplish a certain task such as mathematical, statistical, financial, logical/data calculations, etc. Functions in QBASIC are readymade programs that take some data, manipulate them and return the value, which may be a string or numeric type. Programming languages also have certain functions like spreadsheets or database software.


QBASIC supports two types of functions. They are: –


A function that is written and stored by the programmer to perform a specific task is known as User Defined Functions. When QBASIC does not provide a built-in function to solve any particular problem required by the programmer in that case only programmers define this type of function. FUNCTION……………END FUNCTION statement can be used to define the function. [1] 


The functions which are provided by the QBASIC system and also allow the programmer to use them according to the requirement are known as BUILT-IN or Library Functions. These functions are required to be called by the programmer to use them in a program. Some common Build-IN or Library Functions are LEN, LEFT$, RIGHT$, MID$, UCASE$, LCASE$, CHR$………etc.[2]  Here are the types of library functions:

·   Mathematical Functions

The numerical data is processed using mathematical functions. The following are some of the mathematical functions used in QBASIC:

–        SQR Function

The SQR Function gives the result as the square root of the given number.

Syntax:SQR (number)


–        ABS Function

This function is used to return the absolute value of a number or we can convert negative numbers into positive.



–        MOD Operator

This operator gives the remainder that comes after dividing two given numbers. It is also considered an arithmetic operator.

Syntax: N1 MOD N2

5 MOD 2


–        COS, SIN, and TAN Function

These are trigonometric functions. They are used to find the cosine, sine, and tangent of the given angle.

Syntax: COS (angle), SIN (angle), TAN (angle)

–        INT Function

This Function is used to obtain the largest integer from the given number.

Syntax: INT (number)

  	Num = 5.9999999
  	PRINT INT (pi)


The CINT function gives results by rounding up the fractional portion. It supports only -32768 to +32767.

Syntax: CINT (number)

  	              CINT (12.4278)

String Function

The string functions are used to process string data. Here are some of the string functions used in QBASIC:

–  LEN Function

This function gives output as the length of a given string.

Syntax: LEN (string)

   	A$ = “COMPUTER”
       PRINT LEN (A$)


–    LEFT$

This function retrieves the specified number of characters from the string’s left side.

Syntax: LEFT$ (string, n)

             	A$ = “COMPUTER”
             	PRINT LEFT$ (A$, 5)

–        RIGHT$

This function retrieves the specified number of characters from the string’s right


Syntax: RIGHT$ (string, n)

             	A$= “COMPUTER”
             	PRINT RIGHT$ (A$, 5)


–        LCASE$

This functions changes the capital letters of given function into small letters.

Syntax: LCASE$ (string)

            	A$ = “COMPUTER”
           	PRINT LCASE$ (A$)

–        UCASE$

This function changes small letters of a given function into capital letters.

Syntax: UCASE$

PRINT UCASE$ (“computer”

A)Some more library functions along with their uses are listed below:

1). MID$:

MID$ function returns a specific number of characters from a string.

2). LEN:

LEN function returns the number of characters in a string or the number of bytes required by a variable.

3). LCASE$:

LCASE$ function converts all the uppercase characters in lowercase.

4). UCASE$:

UCASE$ function converts a string to uppercase.

5). ASC:

ASC function converts a character or a string variable to its corresponding ASC II code. Only the first character of a string is evaluated by the ASC function.

6). CHR$:

CHR$ function retrieves the single character represented by the ASC II number.

7). STR$:

STR$ function converts a string expression to its string representation.

8). VAL:

VAL function converts a string expression consisting of digits into a numeric value.

9). LTRIM$:

LTRIM$ function removes leading blanks from the left side of the spring expression.               

10). RTRIM$:

RTRI$ function removes trailing blanks from the right side of the string expression.

11). STRING$:

STRING$ function is used with a PRINT statement to display a particular character a specific number of times.

12). INSTR:

INSTR function returns the position of the first occurrence of a string in another string.

13). DATE$:

DATE$ function returns the current system date of the computer and allows to set the current system date.

14). TIME$:

TIME$ function returns the current system time of the computer and allows to set the current time.

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