c format input to binary and then output

Question

I want to take an user input with the following code:

uint32_t value;
printf("value: ");
scanf("%"SCNu32, &value);

My question now is, how would I use the user input (in my case value) and then return it formatted as a binary number without loops in the function print_binary? The output must be 32bits after the 0b. I can't use any kind of loops anywhere.

#include <inttypes.h>
#include <stdio.h>
#include <stdlib.h>

void print_binary(uint32_t value){

    printf("%d = 0b",value);
    //I want to print the variable value with a fixed length of 32 and that it is 
    //binary with the starting index of 0bBinaryValueOfNumber.
    return;
}

int main(void) {
    uint32_t value;
    printf("value: ");
    if (scanf("%"SCNu32, &value) != 1) {
        fprintf(stderr, "ERROR: While reading the 'uint32_t' value an error occurred!");
        return EXIT_FAILURE;
    }
    printf("\n");
    print_binary(value);
    printf("\n");
    return EXIT_SUCCESS;
}

I do also have the following examples:

If the user input is 5, the function should return "5 = 0b00000000000000000000000000000101".

thanks for the quick solution, unfortunately I'm not allowed to use for loops or while loops. Is there another possibility? — SourceCodeEngineer
– SourceCodeEngineer, Commented Nov 20, 2021 at 16:40

chqrlie · Accepted Answer · 2021-11-20 16:56:10Z

2

If you cannot use loops, you could use recursion:

void print_bin(uint32_t n, int digits) {
    if (digits > 1) print_bin(n >> 1, digits - 1);
    putchar('0' + (n & 1));
}

void print_binary(uint32_t value) {
    printf("%d = 0b", value);
    print_bin(value, 32);
    printf("\n");
}

Alternative approach using tail recursion:

void print_bin(uint32_t n, int digits) {
    putchar('0' + ((n >>-- digits) & 1));
    if (digits > 0) print_bin(n, digits);
}

edited Nov 20, 2021 at 16:56

answered Nov 20, 2021 at 16:48

chqrlie

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3 Comments

chux Over a year ago

Interesting >>-- "operator".

chqrlie Over a year ago

@chux-ReinstateMonica: A dangerous one: a poisonous dart fired from a blowgun. Illegal in many places but not in France

chux Over a year ago

Now I thinking, what the longest "operator" in C? n -->>-- digits is 6. Hmmm.

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