stdio.h
The stdio.h
library in C provides functionalities for input and output operations. Here are some of the important functions provided by stdio.h
with examples:
printf
- Prints formatted output to the standard output (stdout).
-
Syntax:
int printf(const char *format, ...)
#include <stdio.h>
int main() {
printf("Hello, World!\n"); // Output: Hello, World!
printf("Number: %d\n", 10); // Output: Number: 10
return 0;
}
scanf
- Reads formatted input from the standard input (stdin).
-
Syntax:
int scanf(const char *format, ...)
#include <stdio.h>
int main() {
int num;
printf("Enter a number: ");
scanf("%d", &num);
printf("You entered: %d\n", num);
return 0;
}
gets
- Reads a line from stdin into the buffer pointed to by
s
until a newline character or EOF is encountered. -
Syntax:
char *gets(char *s)
#include <stdio.h>
int main() {
char str[100];
printf("Enter a string: ");
gets(str);
printf("You entered: %s\n", str);
return 0;
}
fgets
- Reads a line from the specified stream and stores it into the string pointed to by
s
. Reading stops after ann-1
characters or a newline. -
Syntax:
char *fgets(char *s, int n, FILE *stream)
#include <stdio.h>
int main() {
char str[100];
printf("Enter a string: ");
fgets(str, 100, stdin);
printf("You entered: %s\n", str);
return 0;
}
putchar
- Writes a character to the standard output (stdout).
-
Syntax:
int putchar(int char)
#include <stdio.h>
int main() {
putchar('A'); // Output: A
putchar('\n');
return 0;
}
getchar
- Reads the next character from the standard input (stdin).
-
Syntax:
int getchar(void)
#include <stdio.h>
int main() {
int c;
printf("Enter a character: ");
c = getchar();
printf("You entered: %c\n", c);
return 0;
}
puts
- Writes a string to the standard output (stdout) followed by a newline character.
-
Syntax:
int puts(const char *s)
#include <stdio.h>
int main() {
puts("Hello, World!"); // Output: Hello, World!
return 0;
}
fputs
- Writes a string to the specified stream.
-
Syntax:
int fputs(const char *s, FILE *stream)
#include <stdio.h>
int main() {
fputs("Hello, World!\n", stdout); // Output: Hello, World!
return 0;
}
stdlib.h
The stdlib.h
library in C provides various utility functions for performing general-purpose operations, including memory allocation, process control, conversions, and searching/sorting. Here are some of the important functions provided by stdlib.h
with examples:
malloc
- Allocates a block of memory of a specified size.
-
Syntax:
void *malloc(size_t size)
#include <stdio.h>
#include <stdlib.h>
int main() {
int *arr;
int n = 5;
arr = (int *)malloc(n * sizeof(int)); // Allocates memory for 5 integers
if (arr == NULL) {
printf("Memory allocation failed\n");
return 1;
}
for (int i = 0; i < n; i++) {
arr[i] = i + 1;
}
for (int i = 0; i < n; i++) {
printf("%d ", arr[i]); // Output: 1 2 3 4 5
}
free(arr); // Frees the allocated memory
return 0;
}
calloc
- Allocates a block of memory for an array of elements, initializing all bytes to zero.
-
Syntax:
void *calloc(size_t num, size_t size)
#include <stdio.h>
#include <stdlib.h>
int main() {
int *arr;
int n = 5;
arr = (int *)calloc(n, sizeof(int)); // Allocates memory for 5 integers and initializes to zero
if (arr == NULL) {
printf("Memory allocation failed\n");
return 1;
}
for (int i = 0; i < n; i++) {
printf("%d ", arr[i]); // Output: 0 0 0 0 0
}
free(arr); // Frees the allocated memory
return 0;
}
realloc
- Changes the size of a previously allocated memory block.
-
Syntax:
void *realloc(void *ptr, size_t size)
#include <stdio.h>
#include <stdlib.h>
int main() {
int *arr;
int n = 5;
arr = (int *)malloc(n * sizeof(int)); // Allocates memory for 5 integers
if (arr == NULL) {
printf("Memory allocation failed\n");
return 1;
}
for (int i = 0; i < n; i++) {
arr[i] = i + 1;
}
n = 10; // Resize the array to hold 10 integers
arr = (int *)realloc(arr, n * sizeof(int));
if (arr == NULL) {
printf("Memory reallocation failed\n");
return 1;
}
for (int i = 5; i < n; i++) {
arr[i] = i + 1;
}
for (int i = 0; i < n; i++) {
printf("%d ", arr[i]); // Output: 1 2 3 4 5 6 7 8 9 10
}
free(arr); // Frees the allocated memory
return 0;
}
free
- Frees the previously allocated memory.
-
Syntax:
void free(void *ptr)
#include <stdlib.h>
int main() {
int *arr = (int *)malloc(5 * sizeof(int));
// ... use the allocated memory ...
free(arr); // Frees the allocated memory
return 0;
}
exit
- Terminates the program.
-
Syntax:
void exit(int status)
#include <stdio.h>
#include <stdlib.h>
int main() {
printf("Exiting the program\n");
exit(0); // Exits the program with a status code of 0
printf("This line will not be executed\n");
return 0;
}
string.h
The string.h
library in C provides functions for handling strings and performing various operations on them, such as copying, concatenation, comparison, and searching. Here are some of the important functions provided by string.h
with examples:
strlen
- Computes the length of a string.
-
Syntax:
size_t strlen(const char *str)
#include <stdio.h>
#include <string.h>
int main() {
char str[] = "Hello, world!";
printf("Length of the string: %zu\n", strlen(str)); // Output: Length of the string: 13
return 0;
}
strcpy
- Copies a string to another.
-
Syntax:
char *strcpy(char *dest, const char *src)
#include <stdio.h>
#include <string.h>
int main() {
char src[] = "Hello, world!";
char dest[50];
strcpy(dest, src);
printf("Copied string: %s\n", dest); // Output: Copied string: Hello, world!
return 0;
}
strncpy
- Copies a specified number of characters from a source string to a destination string.
-
Syntax:
char *strncpy(char *dest, const char *src, size_t n)
#include <stdio.h>
#include <string.h>
int main() {
char src[] = "Hello, world!";
char dest[50];
strncpy(dest, src, 5);
dest[5] = '\0'; // Null-terminate the destination string
printf("Copied string: %s\n", dest); // Output: Copied string: Hello
return 0;
}
strcat
- Appends a source string to a destination string.
-
Syntax:
char *strcat(char *dest, const char *src)
#include <stdio.h>
#include <string.h>
int main() {
char dest[50] = "Hello";
char src[] = ", world!";
strcat(dest, src);
printf("Concatenated string: %s\n", dest); // Output: Concatenated string: Hello, world!
return 0;
}
strncat
- Appends a specified number of characters from a source string to a destination string.
-
Syntax:
char *strncat(char *dest, const char *src, size_t n)
#include <stdio.h>
#include <string.h>
int main() {
char dest[50] = "Hello";
char src[] = ", world!";
strncat(dest, src, 7);
printf("Concatenated string: %s\n", dest); // Output: Concatenated string: Hello, world
return 0;
}
strcmp
- Compares two strings.
-
Syntax:
int strcmp(const char *str1, const char *str2)
#include <stdio.h>
#include <string.h>
int main() {
char str1[] = "Hello";
char str2[] = "Hello";
char str3[] = "World";
printf("Comparison result: %d\n", strcmp(str1, str2)); // Output: Comparison result: 0
printf("Comparison result: %d\n", strcmp(str1, str3)); // Output: Comparison result: -1 (or another negative value)
return 0;
}
strncmp
- Compares a specified number of characters of two strings.
-
Syntax:
int strncmp(const char *str1, const char *str2, size_t n)
#include <stdio.h>
#include <string.h>
int main() {
char str1[] = "Hello";
char str2[] = "Helium";
printf("Comparison result: %d\n", strncmp(str1, str2, 3)); // Output: Comparison result: 0
printf("Comparison result: %d\n", strncmp(str1, str2, 5)); // Output: Comparison result: -1 (or another negative value)
return 0;
}
strchr
- Searches for the first occurrence of a character in a string.
-
Syntax:
char *strchr(const char *str, int c)
#include <stdio.h>
#include <string.h>
int main() {
char str[] = "Hello, world!";
char *ptr = strchr(str, 'w');
if (ptr != NULL) {
printf("Character found: %s\n", ptr); // Output: Character found: world!
} else {
printf("Character not found\n");
}
return 0;
}
strrchr
- Searches for the last occurrence of a character in a string.
-
Syntax:
char *strrchr(const char *str, int c)
#include <stdio.h>
#include <string.h>
int main() {
char str[] = "Hello, world!";
char *ptr = strrchr(str, 'o');
if (ptr != NULL) {
printf("Last occurrence of character found: %s\n", ptr); // Output: Last occurrence of character found: orld!
} else {
printf("Character not found\n");
}
return 0;
}
strstr
- Searches for the first occurrence of a substring in a string.
-
Syntax:
char *strstr(const char *haystack, const char *needle)
#include <stdio.h>
#include <string.h>
int main() {
char str[] = "Hello, world!";
char *ptr = strstr(str, "world");
if (ptr != NULL) {
printf("Substring found: %s\n", ptr); // Output: Substring found: world!
} else {
printf("Substring not found\n");
}
return 0;
}
ctype.h
The ctype.h
library in C provides functions for character classification and conversion. These functions help to determine the type of a character (such as whether it is a digit, letter, whitespace, etc.) and to convert characters between different cases.
Here are some of the important functions provided by ctype.h
with examples:
isalpha
- Checks if the given character is an alphabetic letter.
-
Syntax:
int isalpha(int c)
#include <stdio.h>
#include <ctype.h>
int main() {
char ch = 'A';
if (isalpha(ch)) {
printf("%c is an alphabetic letter\n", ch); // Output: A is an alphabetic letter
} else {
printf("%c is not an alphabetic letter\n", ch);
}
return 0;
}
isdigit
- Checks if the given character is a digit.
-
Syntax:
int isdigit(int c)
#include <stdio.h>
#include <ctype.h>
int main() {
char ch = '9';
if (isdigit(ch)) {
printf("%c is a digit\n", ch); // Output: 9 is a digit
} else {
printf("%c is not a digit\n", ch);
}
return 0;
}
isalnum
- Checks if the given character is an alphanumeric character.
-
Syntax:
int isalnum(int c)
#include <stdio.h>
#include <ctype.h>
int main() {
char ch = 'a';
if (isalnum(ch)) {
printf("%c is an alphanumeric character\n", ch); // Output: a is an alphanumeric character
} else {
printf("%c is not an alphanumeric character\n", ch);
}
return 0;
}
isspace
- Checks if the given character is a whitespace character.
-
Syntax:
int isspace(int c)
#include <stdio.h>
#include <ctype.h>
int main() {
char ch = ' ';
if (isspace(ch)) {
printf("The character is a whitespace\n"); // Output: The character is a whitespace
} else {
printf("The character is not a whitespace\n");
}
return 0;
}
isupper
- Checks if the given character is an uppercase letter.
-
Syntax:
int isupper(int c)
#include <stdio.h>
#include <ctype.h>
int main() {
char ch = 'Z';
if (isupper(ch)) {
printf("%c is an uppercase letter\n", ch); // Output: Z is an uppercase letter
} else {
printf("%c is not an uppercase letter\n", ch);
}
return 0;
}
islower
- Checks if the given character is a lowercase letter.
-
Syntax:
int islower(int c)
#include <stdio.h>
#include <ctype.h>
int main() {
char ch = 'z';
if (islower(ch)) {
printf("%c is a lowercase letter\n", ch); // Output: z is a lowercase letter
} else {
printf("%c is not a lowercase letter\n", ch);
}
return 0;
}
toupper
- Converts a given character to its uppercase equivalent if it is a lowercase letter.
-
Syntax:
int toupper(int c)
#include <stdio.h>
#include <ctype.h>
int main() {
char ch = 'a';
char upper = toupper(ch);
printf("Uppercase of %c is %c\n", ch, upper); // Output: Uppercase of a is A
return 0;
}
tolower
- Converts a given character to its lowercase equivalent if it is an uppercase letter.
-
Syntax:
int tolower(int c)
#include <stdio.h>
#include <ctype.h>
int main() {
char ch = 'A';
char lower = tolower(ch);
printf("Lowercase of %c is %c\n", ch, lower); // Output: Lowercase of A is a
return 0;
}
math.h
The math.h
library in C provides functions for mathematical computations. These functions allow operations like trigonometry, logarithms, exponentiation, and more. Here are some important functions provided by math.h
with examples:
Trigonometric Functions
sin
- Computes the sine of an angle (in radians).
-
Syntax:
double sin(double x)
#include <stdio.h>
#include <math.h>
int main() {
double angle = 0.5;
double result = sin(angle);
printf("sin(0.5) = %.4f\n", result); // Output: sin(0.5) = 0.4794
return 0;
}
cos
- Computes the cosine of an angle (in radians).
-
Syntax:
double cos(double x)
#include <stdio.h>
#include <math.h>
int main() {
double angle = 0.5;
double result = cos(angle);
printf("cos(0.5) = %.4f\n", result); // Output: cos(0.5) = 0.8776
return 0;
}
tan
- Computes the tangent of an angle (in radians).
-
Syntax:
double tan(double x)
#include <stdio.h>
#include <math.h>
int main() {
double angle = 0.5;
double result = tan(angle);
printf("tan(0.5) = %.4f\n", result); // Output: tan(0.5) = 0.5463
return 0;
}
Exponential and Logarithmic Functions
exp
- Computes the base-e exponential function of x, e^x.
-
Syntax:
double exp(double x)
#include <stdio.h>
#include <math.h>
int main() {
double x = 2.0;
double result = exp(x);
printf("exp(2.0) = %.4f\n", result); // Output: exp(2.0) = 7.3891
return 0;
}
log
- Computes the natural logarithm (base-e logarithm) of x.
-
Syntax:
double log(double x)
#include <stdio.h>
#include <math.h>
int main() {
double x = 10.0;
double result = log(x);
printf("log(10.0) = %.4f\n", result); // Output: log(10.0) = 2.3026
return 0;
}
pow
- Computes x raised to the power of y (x^y).
-
Syntax:
double pow(double x, double y)
#include <stdio.h>
#include <math.h>
int main() {
double base = 2.0;
double exponent = 3.0;
double result = pow(base, exponent);
printf("pow(2.0, 3.0) = %.4f\n", result); // Output: pow(2.0, 3.0) = 8.0000
return 0;
}
sqrt
- Computes the square root of x.
-
Syntax:
double sqrt(double x)
#include <stdio.h>
#include <math.h>
int main() {
double x = 25.0;
double result = sqrt(x);
printf("sqrt(25.0) = %.4f\n", result); // Output: sqrt(25.0) = 5.0000
return 0;
}
Rounding and Remainder Functions
ceil
- Computes the smallest integer value greater than or equal to x.
-
Syntax:
double ceil(double x)
#include <stdio.h>
#include <math.h>
int main() {
double x = 3.14;
double result = ceil(x);
printf("ceil(3.14) = %.4f\n", result); // Output: ceil(3.14) = 4.0000
return 0;
}
floor
- Computes the largest integer value less than or equal to x.
-
Syntax:
double floor(double x)
#include <stdio.h>
#include <math.h>
int main() {
double x = 3.14;
double result = floor(x);
printf("floor(3.14) = %.4f\n", result); // Output: floor(3.14) = 3.0000
return 0;
}
round
- Rounds x to the nearest integer value.
-
Syntax:
double round(double x)
#include <stdio.h>
#include <math.h>
int main() {
double x = 3.75;
double result = round(x);
printf("round(3.75) = %.4f\n", result); // Output: round(3.75) = 4.0000
return 0;
}
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