What are the predefined functions in C language?

Functions are broadly classified into two types, which are as follows −

• Predefined functions
• User defined functions

Predefined (or) library functions

• These functions are already defined in the system libraries.

• Programmer will reuse the already present code in the system libraries to write error free code.

• But to use the library functions, user must be aware of 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 ( ) present in stdio.h library.
• clrscr ( ) present in conio.h library.

Example

Given below is the C program on predefined function 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 more predefined functions −

• Cbrt(x) :cube root of x
• Log(x) : natural logarithm of x base e
• Ceils(x): round x to smaller integer not less than x
• Pow(x,y): x raised to power y………

Example

Following is a C program using the 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();
}

Output

The output is stated below −

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