#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <openssl/md5.h>

// Hàm tính MD5 hash cho một chuỗi
void calculate_md5_hash(const char* input_string, unsigned char* hash) {
    MD5_CTX context;
    MD5_Init(&context);
    MD5_Update(&context, input_string, strlen(input_string));
    MD5_Final(hash, &context);
}

// Hàm in giá trị băm MD5
void print_md5_hash(const unsigned char* hash) {
    for (int i = 0; i < MD5_DIGEST_LENGTH; i++) {
        printf("%02x", hash[i]);
    }
    printf("\n");
}

// Hàm so sánh hai MD5 hashes
int compare_md5_hashes(const unsigned char* hash1, const unsigned char* hash2) {
    return memcmp(hash1, hash2, MD5_DIGEST_LENGTH) == 0;
}

int main() {
    char user_input[100];
    unsigned char hash_value[MD5_DIGEST_LENGTH];

    // Tính MD5 hash cho một chuỗi nhập từ người dùng và in kết quả ra màn hình
    printf("Nhập một chuỗi: ");
    fgets(user_input, sizeof(user_input), stdin);
    user_input[strcspn(user_input, "\n")] = 0;
    calculate_md5_hash(user_input, hash_value);
    printf("MD5 hash của chuỗi nhập là: ");
    print_md5_hash(hash_value);

    // So sánh hai MD5 hashes
    unsigned char hash1[MD5_DIGEST_LENGTH] = {
        0x09, 0x8f, 0x6b, 0xcd, 0x46, 0x21, 0xd3, 0x73, 0xca, 0xde, 0x4e, 0x83, 0x26, 0x27, 0xb4, 0xf6
    };  // MD5 hash 1
    unsigned char hash2[MD5_DIGEST_LENGTH] = {
        0x5e, 0xb6, 0x3b, 0xbb, 0xe0, 0x1e, 0xee, 0xd0, 0x93, 0xcb, 0x22, 0xbb, 0x8f, 0x5a, 0xcd, 0xc3
    };  // MD5 hash 2

    if (compare_md5_hashes(hash1, hash2)) {
        printf("Hai MD5 hash giống nhau.\n");
    } else {
        printf("Hai MD5 hash khác nhau.\n");
    }

    // Tạo danh sách băm sử dụng MD5
    const char* data[] = {
        "hello", "world", "python", "hash", "exercise"
    };
    int num_data = sizeof(data) / sizeof(data[0]);

    printf("Danh sách băm sử dụng MD5:\n");
    for (int i = 0; i < num_data; i++) {
        calculate_md5_hash(data[i], hash_value);
        printf("%s: ", data[i]);
        print_md5_hash(hash_value);
    }

    return 0;
}

C Language online compiler

Write, Run & Share C Language code online using OneCompiler's C online compiler for free. It's one of the robust, feature-rich online compilers for C language, running the latest C version which is C18. Getting started with the OneCompiler's C editor is really simple and pretty fast. The editor shows sample boilerplate code when you choose language as 'C' and start coding!

Read inputs from stdin

OneCompiler's C online editor supports stdin and users can give inputs to programs using the STDIN textbox under the I/O tab. Following is a sample C program which takes name as input and print your name with hello.

#include <stdio.h>
int main()
{
    char name[50];
    printf("Enter name:");
    scanf("%s", name);
    printf("Hello %s \n" , name );
    return 0;
    
}

About C

C language is one of the most popular general-purpose programming language developed by Dennis Ritchie at Bell laboratories for UNIX operating system. The initial release of C Language was in the year 1972. Most of the desktop operating systems are written in C Language.

Key features:

  • Structured Programming
  • Popular system programming language
  • UNIX, MySQL and Oracle are completely written in C.
  • Supports variety of platforms
  • Efficient and also handle low-level activities.
  • As fast as assembly language and hence used as system development language.

Syntax help

Loops

1. If-Else:

When ever you want to perform a set of operations based on a condition if-else is used.

if(conditional-expression) {
   // code
} else {
   // code
}

You can also use if-else for nested Ifs and if-else-if ladder when multiple conditions are to be performed on a single variable.

2. Switch:

Switch is an alternative to if-else-if ladder.

switch(conditional-expression) {    
case value1:    
 // code    
 break;  // optional  
case value2:    
 // code    
 break;  // optional  
...    
    
default:     
 // code to be executed when all the above cases are not matched;    
}

3. For:

For loop is used to iterate a set of statements based on a condition.

for(Initialization; Condition; Increment/decrement){  
  // code  
}

4. While:

While is also used to iterate a set of statements based on a condition. Usually while is preferred when number of iterations are not known in advance.

while(condition) {  
 // code 
}

5. Do-While:

Do-while is also used to iterate a set of statements based on a condition. It is mostly used when you need to execute the statements atleast once.

do {
  // code 
} while (condition);

Arrays

Array is a collection of similar data which is stored in continuous memory addresses. Array values can be fetched using index. Index starts from 0 to size-1.

Syntax

One dimentional Array:

data-type array-name[size];

Two dimensional array:

data-type array-name[size][size];

Functions

Function is a sub-routine which contains set of statements. Usually functions are written when multiple calls are required to same set of statements which increases re-usuability and modularity.

Two types of functions are present in C

  1. Library Functions:

Library functions are the in-built functions which are declared in header files like printf(),scanf(),puts(),gets() etc.,

  1. User defined functions:

User defined functions are the ones which are written by the programmer based on the requirement.

How to declare a Function

return_type function_name(parameters);

How to call a Function

function_name (parameters)

How to define a Function

return_type function_name(parameters) {  
  //code
}