What does '% 02x' do exactly?

I was seeing some examples of hash functions > from OpenSSL and I came across the format specifier / a> %02x . I do not know very well their purpose we codes that I saw. I even understand that %02x is to fill the field with zeros and 2 is the number of zeros that will have in that fill (I think that).

Well, here's a code developed by me where I had to use (I do not know why I had to use it) %02x :

#include <stdio.h>
#include <string.h>
#include <string.h>
#include <openssl/sha.h>

void get_string(char *string, size_t max_input_size){

    fgets(string, max_input_size, stdin);

    unsigned int len=strlen(string);

    string[len-1]='
Write >FN P90

Digest: 45603ce52cd32a33e3e60c219d0c18e6bd32af24ac39aa000d84e763d23c3031
';
}

int main(void){

    char string[50];
    unsigned char digest[SHA256_DIGEST_LENGTH];

    printf("Write >");
    get_string(string, 50);

    SHA256((unsigned char*)string, strlen(string), digest);

    char stringMD[SHA256_DIGEST_LENGTH*2+1];

    for(unsigned int i=0; i<SHA256_DIGEST_LENGTH; i++){

        sprintf(&stringMD[i*2], "%02x", (unsigned int)digest[i]);
    }

    printf("\n\nDigest: %s\n\n", stringMD);

    return 0;
}

Execution (with %02x ):

Write >FN P90

Digest: 45603ce52cd32a33e3e6c

Execution (with only %x ):

#include <stdio.h>
#include <string.h>
#include <string.h>
#include <openssl/sha.h>

void get_string(char *string, size_t max_input_size){

    fgets(string, max_input_size, stdin);

    unsigned int len=strlen(string);

    string[len-1]='
Write >FN P90

Digest: 45603ce52cd32a33e3e60c219d0c18e6bd32af24ac39aa000d84e763d23c3031
';
}

int main(void){

    char string[50];
    unsigned char digest[SHA256_DIGEST_LENGTH];

    printf("Write >");
    get_string(string, 50);

    SHA256((unsigned char*)string, strlen(string), digest);

    char stringMD[SHA256_DIGEST_LENGTH*2+1];

    for(unsigned int i=0; i<SHA256_DIGEST_LENGTH; i++){

        sprintf(&stringMD[i*2], "%02x", (unsigned int)digest[i]);
    }

    printf("\n\nDigest: %s\n\n", stringMD);

    return 0;
}

However, what is the purpose of %02x ?