C - Int Array to Integer with Mixed Digit Numbers

Question

I need to convert an integer array of size 4 into an int. I've seen solutions for int arrays that look like {1, 2, 3, 4} turn into 1234, and I've also seen ones where an array like {10, 20, 30} would turn into 102030. However, my problem is that I'll have an array that might look like {0, 6, 88, 54} and the solutions I previously mentioned only work on arrays with ints of the same type {e.g all one digit or all two digit}.

What should I do to solve this?

My expected output from the {0, 6, 88, 54} array would be 68854.

Examples An output with zeros in the middle should keep them, i.e. {6, 0, 0, 8} would be 6008 but {0, 6, 0, 0, 8} by default would still be 6008 in int form. I need this in an int but I wouldn't mind having a string intermediate.

I would use itoa on each element of the array and then use strcat to append each string to the output string. — bruceg
– bruceg, Commented Mar 24, 2018 at 0:26
Right. So what would the expected output be for [6, 0, 0, 8]? — SeverityOne
– SeverityOne, Commented Mar 24, 2018 at 0:27
An output with zeros in the middle should keep them, ie {6, 0, 0, 8} would be 6008 but {0, 6, 0, 0, 8} by default would still be 6008 in int form. I need this in an int but I wouldn't mind having a string intermediate — bmw417
– bmw417, Commented Mar 24, 2018 at 0:35

score 2 · Accepted Answer · 2018-03-24 00:29:51Z

2

You could do something like this:

int res = 0;
int nums[4] = {1, 4, 3, 2}

int i = 0, temp;
for (i = 0; i < 4; ++i) {
  temp = nums[i];
  do {
    res *= 10;
  } while ((temp /= 10) > 0);


  res += nums[i];
}

edited Mar 24, 2018 at 0:29

answered Mar 24, 2018 at 0:21

user5550963

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4 Comments

bmw417 Over a year ago

This doesn't work on mixed digit numbers, only single digit numbers

Pablo Over a year ago

@bmw417 for me it's not clear what number you expect from {0, 6, 88, 54}

bmw417 Over a year ago

It would be 68854

user5550963 Over a year ago

@bmw417 so I have fixed the answer and it works even with this weird example Pablo gave as an example.

Pablo · Accepted Answer · 2018-03-24 00:38:22Z

1

What about this solution?

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

int main(void)
{
    int arr[] = {0, 6, 88, 54};

    char buffer[1000] = { 0 };

    for(size_t i = 0; i < sizeof arr / sizeof *arr; ++i)
        sprintf(buffer, "%s%d", buffer, arr[i]);

    int val = strtol(buffer, NULL, 10);
    printf("%d\n", val);

    return 0;
}

int prints 608854.

answered Mar 24, 2018 at 0:38

Pablo

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Comments

tom · Accepted Answer · 2018-03-24 00:41:00Z

1

a neat solution would perhaps be to print to a string then convert the string back to an integer

char dummy[100];
int answer;
int input[4];

....

sprintf(dummy,"%d%d%d%d",input[0],input[1],input[2],input[3]);
answer=atoi(dummy);

the sprintf prints your integers into a string

the atoi converts the string into your integer, and it should be able to handle a 0 at the front.

full program

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

int main()
{
  char dummy[100];
  int answer;
  int input[4]={3,4,0,345};

  sprintf(dummy,"%d%d%d%d",input[0],input[1],input[2],input[3]);
  answer=atoi(dummy);

  printf("%d\n",answer);

  return 0;
}

edited Mar 24, 2018 at 0:41

answered Mar 24, 2018 at 0:35

tom

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