What are the predefined functions in C language?

Functions are roughly divided into two categories, as follows: -

• Predefined functions
• User-defined functions

Predefined (or) library functions

• These functions have been defined in the system library.

• Programmers will reuse code already in system libraries to write error-free code.

• But to use library functions, users must understand the syntax of the function.

Example-

• sqrt() function is available in math.h library and its usage is-

y= sqrt (x)
x number must be positive
eg: y = sqrt (25)
then ‘y’ = 5

• printf ( ) exists in the stdio.h library.
• clrscr ( ) exists in the conio.h library.

Example

The following is a C program of predefined functions sqrt, printf, conio-

#include<stdio.h>
#include<conio.h>
#include<math.h>
main ( ){
   int x,y;
   clrscr ( );
   printf ("enter a positive number");
   scanf (" %d", &x)
   y = sqrt(x);
   printf("squareroot = %d", y);
   getch();
}

Output

You will see the following output -

Enter a positive number 25
Squareroot = 5

Consider some of the more predefined functions -

• Cbrt(x): Cube root of x
• Log(x): The natural logarithm of the base of .
• Pow(x,y): x raised to the y power...
• ul>
ExampleThe following is a C program using predefined functions-

#include<stdio.h>
#include<math.h>
main ( ){
   int x,y,z,n,k,p,r,q;
   printf ("enter x and n values:");
   scanf (" %d%d", &x,&y)
   y=cbrt(x);
   z=exp(x);
   k=log(x);
   p=ceil(x);
   q=pow(x,r);
   printf("cuberoot = %d", y);
   printf("exponent value = %d",z);
   printf("logarithmic value = %d", k);
   printf("ceil value = %d", p);
   printf("power = %d", q);
   getch();
}

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Output
The output is as follows-

enter x and n values:9 2
cuberoot = 2
exponent value = 8103
logarithmic value = 2
ceil value = 9
power = 81

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