Library Functions in C

Library functions are those functions which are pre-defined by compiler of C language. Some of the library functions are given below:

1. Input / Output function (define in standard input/output stdio.h)
   Input/Output function is define in stdio.h header file. In C language 3 Input and 3 Output function are available for input and output of any data.
   Input Function
• getchar()
  getchar() function is used to take single input charater data.
  Syntax: variable name=getchar();
  Example: x=getchar();
• gets()
  gets() function is used to take multiple input charater data.
  Syntax: gets(variable name);
  Example: gets(name);
• scanf()
  scanf() function is used to take all type of input data such sas (character data , string data , numric data).
  Syntax: scanf("Control string",&variable1,&variable2.....);
  Example: scanf("%d%f",&x,&y);

Output Functions
• putchar()
  putchar() function is used to print single charater data. It is output function.
  Syntax:putchar(variable name);
  Example: putchar(x);
• puts()
  puts() function is used to print multiple character data (string).
  Syntax: puts(variable name);
  Example: puts(name);
• printf()
  printf() function is used to print all type of data such as (character data , string data , numric data) on the screen.
  Syntax: printf("Control string",variable1,variable2.....);
  Example: printf("sum=%d",sum);
                   printf("sum of number",sum);
                   printf("%d",sum);
1. Mathematical Function (define in math.h)
   These functions are used for mathematical operation.Include "math.h" header file before main() function for using these functions. These functions are:
   • sqrt():This function is used to find out square root of any number.
     Syntax: sqrt(argument);
     Example: sqrt(x);
   • pow(): pow() function is to find power of any number.
     Syntax: pow(argument1 , argument2);
     Example: pow(x,y); (i.e x^y)
   • abs(x): This function return absolute number (positive number) of any numeric number.
     Syntax: abs(argument);
     Example: abs(-10); (i.e return 10)
2. String function
   String function is used to manipulate or format the sting. String is a group of characters. Include "string.h" header file before main() function for using these functions.These functions are :
   • strlen(): This function is used to return the length of string.
     Syntax: strlen(argument);
     Example: x=strlen("Hello");
   • strcat(): This function is used to concate two string.
     Syntax: strcat(s1 , s2));
     Example: x=strlen("Hello" , "world");
   • strcpy(): This function is used to copy one string into second string.
     Syntax: strcpy(s1 , s2));
     Example: x="hello"; y="world"; strcpy(x , y);
   • strcmp(): This function is used to compair the length between two string.
     Syntax: strcmp(s1 , s2)); (i.e return 0 for s1=s2 , -1 for s1s2)
     Example: x=strcmp("hello" , "Helloworld"); return -1