SHA256 Hash Program (Hex)

Task

Write a program in main.c that takes space-separated strings as command-line arguments, and for each one calculates the SHA256 hash and prints the first 4 bytes of the hash in hexadecimal, prefixed by 0x and followed by a newline. If no strings are passed as arguments, nothing should be printed in the output.

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Example

$ gcc main.c -o main -lcrypto
$ ./main secret password
0x2bb80d53       # output line for secret whose hash starts with "2bb80d.."
0x5e884898       # output line for password whose hash starts with "5e8848.."

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Code

#include <stdio.h>
#include <stdint.h>
#include <string.h>
#include <openssl/sha.h>
 
int main(int argc, char** argv){
    for(int i = 1; i < argc; i++){
	unsigned char hash[32];
	SHA256((unsigned char*)argv[i], strlen(argv[i]), hash);
 
	printf("0x%02x%02x%02x%02x\n", hash[0], hash[1], hash[2], hash[3]);
    }
}