Decimal to binary conversion in C language using ASCII table

Question

I have to make a program that reads some characters and "transform" each character into its corresponding number in the ASCII table and then turn that number into binary and store it in an array. My code so far is:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main(){
int i;
char mensagem[200];
    printf("Digite a mensagem: ");
        setbuf(stdin, NULL); // limpando o buffer antes de digitar a msg
        fgets(mensagem, 200, stdin); // leitura OK

int tamanho = strlen(mensagem); // pega a quant de caracteres (incluindo '\n')
// vetor de inteiros p/ armazenar os valores correspondentes dos caracteres na tabela ASCII
char *num_corresp_int; 
/* aloca um vetor de inteiros p/ os num correspondentes dos caracteres*/
    num_corresp_int =  malloc((tamanho) * sizeof(char)); 
        
    for(i = 0; i < tamanho; i++){
        num_corresp_int[i] = mensagem[i]; // não está passando o '\0'
    }

char *vetor_binario; // aloca um vetor p/ armazenar os valores em binario
/* char pq preciso de apenas 1 byte p/ representar os números 0 e 1*/
    vetor_binario = malloc((tamanho) * sizeof(char)); 
        
int r;
/* (tamanho * 8) pq alocacarei um bit em cada posicao do vetor_binario*/
int a, j, aux = tamanho * 8; 
    for(i = 7, a = 0, j = 0; i >= 0 && j < aux; j++, i--) {
        r = num_corresp_int[a] >> i;
            if(r & 1) {
                vetor_binario[j] = 1;
            } else {
                vetor_binario[j] = 0;
            }
        if(i == 0){
            a++;
            i = 7;
        }else if(a == tamanho){
            break;
        }
    }

    for(i = 0; i < aux; i++){ // Testar se o armazenamento está sendo feito corretamente
        printf("%d", vetor_binario[i]); 
    }
  printf("\n");
  return 0;
}

So my question is on how to define the full stop condition in the loop:

for(i = 7, a = 0, j = 0; i >= 0 && j < aux; j++, i--) {
        r = num_corresp_int[a] >> i;
            if(r & 1) {
                vetor_binario[j] = 1;
            } else {
                vetor_binario[j] = 0;
            }
        if(i == 0){
            a++;
            i = 7;
        }else if(a == tamanho){
            break;
        }
}

Where the total stop of loop (break) will happen when a, which is used to reach the tamanho the message is equal to tamanho. I think this total stop should look like the one I outlined using if and else if.

Example: If typed A and B on the keyboard, the vector num_corresp_int[0] = 65 and num_corresp_int[1] = 66. And so, the vetor_binario of position [0]to [7]shall store the following corresponding numbers of the ASCII table: 01000001 and, of the position [8]to [15] the following numbers: 01000010. That is, every 8 positions of the vetor_binario we will have together (sequentially) to binary representation of a decimal number of ASCII table between 0 and 255.

Program output now if typed AB on the keyboard:

010000011000010000101000

Let’s see: With the above output, in addition to others I tested, I saw that the program stores the 8 bits of the first character (A) correctly, but already p/ the second character (B) and later, the vetor_binario does not store the 1st bit of characters, only from the 2nd bit onwards. OBS: in this given example, the bits after last bit of the character B are corresponding to the \n, being the last two bits (00) remains that I still don’t know how to remove.

Doubts

• How to define the full stop condition in the loop?
• How to solve the problem, where from the 2nd character, the 1st bit is not being stored, and the last bits are over?

Answer 1

The code is confusing, does a lot of unnecessary things. The question is extensive, but little useful information. One of the reasons you have difficulty is the code is too complex. Even the most experienced ones don’t get along with complicated code. I would do so:

#include <stdio.h>
#include <string.h>

int main(){
    char mensagem[200];
    printf("Digite a mensagem: ");
    fgets(mensagem, 200, stdin);
    mensagem[strcspn(mensagem, "\n")] = 0;
    int tamanho = strlen(mensagem);
    char vetor_binario[tamanho * 8 + 1];
    vetor_binario[tamanho * 8 + 1] = '\0';
    for (int i = 0; i < tamanho; i++) {
        for (int j = 7; j >= 0; j--) vetor_binario[i * 8 + (7 - j)] = ((mensagem[i] >> j) & 1) + '0';
    }
    printf("%s", vetor_binario);
}

Behold working in the ideone. And in the repl it.. Also put on the Github for future reference.