Member Avatar for revenge2

hello there, I am working on a small c program that automatically detects whether the input given is a decimal number or a binary number and coverts accordingly.

what is the best way to convert a binary number to a decimal number and a decimal number to a binary number.

i found this to be the easiest when converting from binary to deicmal
http://www.wikihow.com/Convert-from-Decimal-to-Binary

but my program doesnt work..?

/*decimal to binary*/
#include <stdio.h>
int main() {
	int dec;
	int hold=0;
	printf("decimal number : ");
	scanf("%d",&dec);
	
	hold=dec%2;
	
	while (hold!=1){
		if (hold == 0){
			printf("0");
		}else if(hold >1){
			printf("1");
		}else{
			printf("1");
		}
		hold=hold%2;
	}
}

what have i done wrong?

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  • 5 Replies
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  • 7 Months Discussion Span
  • Latest Post Latest Post by akirue09

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Generated

The thread already highlights the two root causes: the algorithm must both remove the bit just read and print digits in the correct order (as and pointed out), and common C errors (missing & in scanf, wrong loop conditions) cause undefined behavior. ’s byte-wise print is useful when an 8-bit view is wanted, but a general converter should produce a minimal-width binary string and accept arbitrary-length binary input.

A compact, robust example follows. It accepts a line of input and treats it as a decimal number unless it’s a binary string (optionally prefixed with 0b); decimal->binary uses shifting and a small buffer, binary->decimal accumulates by left-shifting. The code checks input characters and handles zero.

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

void print_binary_ull(unsigned long long n) {
    if (n == 0) { putchar('0'); putchar('\n'); return; }
    char buf[65];
    int i = 0;
    while (n) {
        buf[i++] = (n & 1) ? '1' : '0';
        n >>= 1;
    }
    while (--i >= 0) putchar(buf[i]);
    putchar('\n');
}

unsigned long long binary_to_ull(const char *s) {
    unsigned long long v = 0;
    for (; *s; ++s) {
        if (*s != '0' && *s != '1') break;
        v = (v << 1) | (unsigned long long)(*s - '0');
    }
    return v;
}

int main(void) {
    char line[128];
    if (!fgets(line, sizeof line, stdin)) return 0;
    line[strcspn(line, "\r\n")] = '\0';
    const char *p = line;
    if (p[0] == '0' && (p[1] == 'b' || p[1] == 'B')) p += 2;
    int is_bin = (*p != '\0');
    for (const char *q = p; *q; ++q) if (*q != '0' && *q != '1') { is_bin = 0; break; }
    if (is_bin) {
        unsigned long long val = binary_to_ull(p);
        printf("%llu\n", val);
    } else {
        char *end;
        unsigned long long dec = strtoull(line, &end, 10);
        print_binary_ull(dec);
    }
    return 0;
}

Troubleshooting notes: missing & in scanf is a frequent cause of crashes (seen in ’s post). Prefer fgets + parsing to avoid buffer/format issues. For very large inputs, validate overflow (functions like strtoull set errno on overflow). For fixed-width output (always 8/16/32 bits) the bitmask approach from is appropriate; for minimal-length binary the buffering-and-reverse method above is clearer. Compile with warnings enabled (e.g., gcc -Wall -Wextra) to catch simple mistakes early.

Recommended Answers

All 5 Replies

Member Avatar for Hiroshe

You don't have any divide's in there. You can't just use modulo for the whole thing. Also, you forgot to read the number backwards.

Member Avatar for ambarisha.kn 
/*decimal to binary*/
#include <stdio.h>

void printBinary(const unsigned char val) {

  for(int i = 7; i >= 0; i--)

    if(val & (1 << i))

     printf("1");

    else

      printf("0");
  printf("\n");

} 

int main() {
	int dec;
	int hold=0;
	printf("Integer number : ");
	scanf("%d",&dec);
	printBinary((unsigned char)dec);	
}
commented: 1. Don't give away free code. 2. That code is bad. -1
Member Avatar for revenge2

hmmm why doesn't this work?

#include <stdio.h>

void bin_c(int x);

int main(){
	int x;
	printf("Enter a number:");
	scanf("%d",x);
	
	bin_c(x);
	return 0;
}

void bin_c(int x){
	
	if (x == 1){
		printf("1");
	}
	
	while (x!=1){
		int y;
		y=x/2;
		if (y == 0){
			printf("0");
		}
		if (y > 1){
			printf("1");
		}
		if (y == 1){
			printf("1");
		}
		bin_c(y);
	}
	
}

i know i have to reverse the order but this doesnt work why is this?

Member Avatar for WaltP

To get a binary value from a decimal value v = val %2; -- v will contain the value of the ones digit. Then, after you get the digit, remove it to get the next digit: v = val /2; Loop until val is 0.

Member Avatar for akirue09

could you pls. do me a program that converting a binary to decimal or decimal to binary with a simple codes in turbo c, which i can easily understand.. for example i will enter an number 1 then it will be automatically to convert it to its binary value. thank u! i will wait for your help! pls. help me..

Edited by WaltP because: Leaving this hijack post here because the answer is in this thread. Maybe you can figure it out if you start reading.
commented: What a BOZO! With the answer right in this thread you have to post this message? -2
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