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Ceil function in C


In the C Programming Language, the ceil function is a library function which is used to obtain the ceil value, i.e., it returns the smallest integer that is greater than or equal to x (i.e., rounds up the nearest integer).

The C library function double ceil(double x) returns the smallest integer value greater than or equal to x.


The ceil function is declared using the keyword ‘ceil’. The following statement is the declaration for ceil() function.

double ceil(double x)


  • x - This is the floating point value.

Return Value

This function returns the smallest integral value not less than x.

Program 1:

#include <stdio.h>  // header files
#include <math.h>

int main () {
 float val1, val2, val3, val4;  // declaring the local variables

   val1 = 1.6;
   val2 = 1.2;
   val3 = 2.8;
   val4 = 2.3;
   printf ("value1 = %.1lf\n", ceil(val1));
   printf ("value2 = %.1lf\n", ceil(val2));
   printf ("value3 = %.1lf\n", ceil(val3));
   printf ("value4 = %.1lf\n", ceil(val4));


Program 2 :

#include <stdio.h>  // header files
#include <math.h>
int main(int argc, const char * argv[])
    double value;  // declaring the temporary variables 
    double result;
    value = 1.6;   // Assigning the value we will find the ceil of 
  result = ceil(value);   // Calculating the ceil of value 
  printf("The ceil of %f is %f\n", value, result);   // printing the result of the calculation 

    return 0;

The ceil function is a library function in C and is used to solve mathematical problems in C. The ceil function is used to solve approximation problems which comes handy when the programmer tries to enter that part of mathematical aspects. To get the broad idea of how these functions work, let’s try to understand more about the library functions in C.

What are library functions?

Library functions are the built-in functions (functions provided by the system) which are stored in the library. The library is the common location where these functions are grouped together and placed.

Each function in the library performs a specific task(operation) and is there to make things easy for the programmer.

The library functions are prototyped and defined at the time of designing the compiler and are present in their respective header files.

Eg: The main() function, printf() function etc. are some of the commonly used functions that are basically the library functions in C.

* The header files are implemented in the C program using the following command,


For eg: #include<stdio.h>, #include<conio.h> …

* If we do not use the header files, the program will throw an error.

For eg: In order to use the printf() function, <stdio.h> should be included in order to print the desired output.

Header File Functions

Most of us are aware of various header files or library functions as they are often used while programming in C. Following is a list of commonly used library functions and the library files in which they are included

Header FileMeaningLibrary Functions
<stdio.h>Standard input-output headerprintf(),scanf(),getchar(c), putchar(s) etc.
<conio.h>Console input-output headerclrscr() , getch() etc.
<stdlib.h>Standard library headercalloc() and malloc()
<math.h>Math header (carry out mathematical calculations)sqrt(d),pow(d1,d2) etc.
<string.h>String header (performs operations on strings)strcpy,strlen,strrev etc.
<ctype.h>Character type header (carry out operations on character)isdigit(), tolower() , toupper() etc.

Program 3: use of <math.h> header file and use of sqrt() library functions

#include <stdio.h>  // header files
#include <math.h>

int main()
   float num, sq_root;  // declaring the local variables
   printf("Enter a number: ");
   scanf("%f", &num);

   sq_root = sqrt(num);  // computes the square root of num and stores in root.

   printf("Square root of %.2f = %.2f", num, sq_root);
   return 0;


Accessing Library Function

A library function can be accessed by following the simple steps;

  1. Writing the function name
  2. Writing the list of arguments

 (a) The arguments must be enclosed in brackets. They must be separated by commas.

 (b) There may be no arguments (in some cases)

Eg: pow (p1,p2) ? arguments enclosed in brackets and separated by commas


Function name

Significance/ Advantages of library function

The major reason to use library functions is that they make the work of a programmer easy, the programmer can simply use the pre-existing codes available in the compiler and need not worry about declaring and defining his own code in order to perform certain basic functions.

The other advantages of using library functions are as follows:

  • Flexibility
  • Performance optimized
  • Time-saving
  • Portability and reliability