clrscr: Clears the screen.
delline: Deletes the line where the cursor is located.
clreol: Clears the portion of the line from the cursor position to the end of the line.
insline: Inserts an empty line.
textcolor: Defines the text color on the screen (colors range from 0 to 15).
textbackground: Defines the background color on the screen.
lowvideo: Diminishes the appearance of the text.
highvideo: Enhances the appearance of the text.
normvideo: Resets the text to normal appearance.
wherex: Returns the horizontal position of the cursor on the text screen.
wherey: Returns the vertical position of the cursor on the text screen.
gotoxy: Positions the cursor on the text screen at the specified coordinates (x, y).
kbhit: Checks if any key is pressed.
cprintf: Prints formatted output.
cscanf: Reads formatted input.
strlen Returns the number of characters in the given string.
strlwr: Converts all characters in the given string to lowercase.
strupr: Converts all characters in the given string to uppercase.
strrev: Reverses the given string.
strcat: Appends the source string to the end of the destination string.
strcmp: Compares two strings.
strstr: Searches for the second string within the first string and returns the address of the first occurrence.
strchr: Searches for a character within the string and returns its address.
abs: Returns the absolute value of the given integer.
cos: Returns the cosine of the given angle in radians.
sin: Returns the sine of the given angle in radians.
tan: Returns the tangent of the given angle in radians
pow: Exponential power function.
log: Returns the logarithm of the given number.
sqrt: Returns the square root of the given parameter.
ceil: Rounds up to the nearest integer.
floor: Rounds down to the nearest integer.
gets: Reads a string from the input device.
puts: Writes a string to the output device.
getw: Reads an integer from a file.
putw: Writes an integer to a file.
getc: Reads a single character from a file.
putc: Writes a single character to a file.
clock: Retrieves the current system time information when called.
time: Returns the current time information in seconds.
settime: Modifies the system time information.
gettime: Retrieves the system time information.
delay: Pauses the program for the specified number of milliseconds.
sleep: Pauses the program for the specified number of seconds.
sound: Produces sound from the PC's sound generator at the specified frequency.
atoi: Converts a string to an integer.
atol: Converts a string to a long integer.
atof: Converts a string to a floating-point number.
itoa: Converts an integer to a string.
div: Used in integer division operations.
max and min: Returns the greater and smaller of two integers, respectively.
rand: Generates a random number.
random: Generates a random integer within a specified range.
randomize: Initializes the random number generator.
exit: Terminates the program.
toupper: Converts the given parameter to uppercase.
tolower: Converts the given parameter to lowercase.
toascii: Converts the given parameter to a code between 0 and 127.
isprint: Returns true if the character is printable.
isalpha: Returns true if the given value is a letter.
isdigit: Returns true if the given value is a digit.