What are the predefined functions in C language?

In C programming, functions are classified into two main types −

• Predefined functions (Library functions)
• User-defined functions

Predefined functions are pre-written functions available in C standard libraries. They provide ready-to-use functionality for common programming tasks, helping developers write efficient and error-free code.

Syntax

#include <library_name.h>
return_type function_name(parameters);

Key Features of Predefined Functions

• Already defined in system libraries
• Tested and optimized for performance
• Reduce development time and effort
• Require appropriate header file inclusion
• Follow standard syntax and conventions

Common Mathematical Functions

The math.h library provides various mathematical functions −

Example: Basic Mathematical Functions

Here's a program demonstrating common predefined functions −

#include <stdio.h>
#include <math.h>

int main() {
    double x = 25.0, y = 3.0;
    
    printf("Original number: %.1f
", x);
    printf("Square root: %.2f
", sqrt(x));
    printf("Power (%.1f^%.1f): %.2f
", x, y, pow(x, y));
    printf("Ceiling of 4.3: %.1f
", ceil(4.3));
    printf("Floor of 4.8: %.1f
", floor(4.8));
    
    return 0;
}

Original number: 25.0
Square root: 5.00
Power (25.0^3.0): 15625.00
Ceiling of 4.3: 5.0
Floor of 4.8: 4.0

Example: String Functions

The string.h library provides string manipulation functions −

#include <stdio.h>
#include <string.h>

int main() {
    char str1[50] = "Hello";
    char str2[50] = "World";
    char str3[100];
    
    printf("String 1: %s
", str1);
    printf("String 2: %s
", str2);
    printf("Length of str1: %lu
", strlen(str1));
    
    strcpy(str3, str1);
    strcat(str3, " ");
    strcat(str3, str2);
    printf("Concatenated: %s
", str3);
    
    return 0;
}

String 1: Hello
String 2: World
Length of str1: 5
Concatenated: Hello World

Common Library Functions by Category

Conclusion

Predefined functions in C provide essential functionality through standard libraries, making programming more efficient and reliable. They eliminate the need to write common operations from scratch and ensure consistent, optimized performance across different platforms.