Combing two integers into 1?

Question

I'm a beginner using C. I want to combine two integers into 1. See example code.

#include <stdio.h>

int main()
{
    int age[4];
    int mouse[4];
    mouse[0]=50;
    age[0]=23;

    age[1]=mouse[0]age[0];

    printf("%d",age[1]);
    return 0;
}

As you can see, I have 50 in mouse[0], 23 in age[0], and i want age[1] to be 5023.

What is the simplest way to do this? This will be a small part of a large code so I really want to keep it simple. And excuse the silly variable names!

Thanks all!

If you search for the very expression "combining two integers into one", you will get tens of hits. — , Sep 13 '13 at 20:17
Candidate for worst question title ever..."combining integers"... — Nick T, Sep 13 '13 at 20:23

Sergey Kalinichenko · Answer 1 · 2013-09-14T10:04:03.013

2

You cannot concatenate integers like that: you need to do it through some elementary math.

Think of "combining" as multiplication followed by addition:

age[1] = mouse[0]*100 + age[0];

Here is how it works:

A = 23
B = 50, B*100 = 5000

    23
+ 5000
------
  5023

Note that this trick works only when the second number has exactly two digits. When the second number has N digits, you need to multiply the first number by the N-th power of ten before performing the addition.

edited Sep 14 '13 at 10:04

answered Sep 13 '13 at 20:18

Sergey Kalinichenko

714,442
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1,110
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Silly arithmetic error: you have an extra zero – recursion.ninja Sep 13 '13 at 21:51

tlehman · Answer 2 · 2013-09-13T20:24:42.497

0

age[1] = 1000*mouse[0] + age[0]

If you want a more general solution, one that doesn't depend on mouse[0] being two digits, you could define a function to get the number of digits:

int digits(int num) {
    return ceil(log10(num));
}

Then you could combine the integers like so:

age[1] = ((int)pow(10, digits(mouse[0])))*mouse[0] + age[0];

edited Sep 13 '13 at 20:24

answered Sep 13 '13 at 20:18

tlehman

5,125
2
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Constablebrew · Answer 3 · 2013-09-13T20:28:22.763

0

I think you meant age[1]=mouse[0]age[0]; to be age[1]=mouse[0]+age[0]; If you can always be sure of the magnitude of the two numbers (e.g. two digits) then just multiply by 100 to shift the digits over age[1]=mouse[0] * 100 + age[0];

If you don't know the exact digits, then you can calculate how much you have to shift the value over by using log10:

age[1] = mouse[0] * (int)pow(10, (int)log10(age[0])) + age[0];

edited Sep 13 '13 at 20:28

answered Sep 13 '13 at 20:20

Constablebrew

816
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7
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score 0 · Answer 4 · answered Sep 13 '13 at 20:47

Since OP is doing a string concatenation, covert to text, concatenate and then back to int.

char buf1[64+64];
char buf2[64];
sprintf(buf1, "%d", mouse[0]);
sprintf(buf2, "%d", age[0]);
strcat(buf1, buf2);
age[1] = atoi(buf1);

There are a number of ways to convert int into text, sprintf() is simple one handy one. Also a number of wasy to convert text to an int. You have to watch out for the - sign and buffer overflow.

score 0 · Answer 5 · answered Sep 13 '13 at 20:56

It seems you are interested in concatenating the textual representation of two ints.

int mouse = 50;
int age = 23;

char combi[BUFSIZ];/*char array to contain the "combination"*/

/*print two ints together in one c-string*/
snprintf(combi, BUFSIZ, "%d%d", mouse,age);
printf("value = %s\n", combi); /*print as string*/

This would print value = 5023 to your terminal, in some interpreted languages one might concatenate strings more easily and the textual and numerical representation are converted automagically, however in C this needs to be done very carefully.

Combing two integers into 1?

5 Answers5