#include <stdio.h>
#include <string.h> //strlen
 
int main()
{
    // para loop "for"
    int i;
 
    // area de entrada
    char hex[] = "6f69";
    int sizeHex = strlen(hex);
 
    // area de saida
    char text[10];
 
    // variaveis de conveniencia
    char ch, high, low;
 
    // trata todos os caracteres da area de entrada
    for (i = 0; i < sizeHex; i += 2)
    {
       high = hex[i];
       high -= 0x30;
       if (high > 9) high -= 7;
       high <<= 4;
 
       low = hex[i+1];
       low -= 0x30;
       if (low > 9) low -= 7;
 
       ch = high | low;
 
       // transfere para area de saida            
       text[i/2] = ch;
    }
 
    text[i/2] = 0; // para delimitar string
 
    printf("string hexadecimal: %s\n",text);
}

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