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.
TYPES OF FUNCTIONS: –
QBASIC supports two types of functions. They are: –
A) USER-DEFINED FUNCTIONS: –
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. 
B) BUILD-IN OR LIBRARY FUNCTIONS: –
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. 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.
PRINT SQR (49)
– ABS Function
This function is used to return the absolute value of a number or we can convert negative numbers into positive.
PRINT ABS (-5)
– 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)
Example: CLS Pi=22/7 Num = 5.9999999 PRINT PI PRINT INT (pi) END
The CINT function gives results by rounding up the fractional portion. It supports only -32768 to +32767.
Syntax: CINT (number)
CLS CINT (12.4278) END
· 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)
CLS A$ = “COMPUTER” PRINT LEN (A$) END
This function retrieves the specified number of characters from the string’s left side.
Syntax: LEFT$ (string, n)
CLS A$ = “COMPUTER” PRINT LEFT$ (A$, 5) END
This function retrieves the specified number of characters from the string’s right
Syntax: RIGHT$ (string, n)
CLS A$= “COMPUTER” PRINT RIGHT$ (A$, 5) END
This functions changes the capital letters of given function into small letters.
Syntax: LCASE$ (string)
CLS A$ = “COMPUTER” PRINT LCASE$ (A$) END
This function changes small letters of a given function into capital letters.
PRINT UCASE$ (“computer”
A)Some more library functions along with their uses are listed below:
MID$ function returns a specific number of characters from a string.
LEN function returns the number of characters in a string or the number of bytes required by a variable.
LCASE$ function converts all the uppercase characters in lowercase.
UCASE$ function converts a string to uppercase.
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.
CHR$ function retrieves the single character represented by the ASC II number.
STR$ function converts a string expression to its string representation.
VAL function converts a string expression consisting of digits into a numeric value.
LTRIM$ function removes leading blanks from the left side of the spring expression.
RTRI$ function removes trailing blanks from the right side of the string expression.
STRING$ function is used with a PRINT statement to display a particular character a specific number of times.
INSTR function returns the position of the first occurrence of a string in another string.
DATE$ function returns the current system date of the computer and allows to set the current system date.
TIME$ function returns the current system time of the computer and allows to set the current time.
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