How to convert an int to string in C?

EDIT: As pointed out in the comment, itoa() is not a standard, so better use sprintf() approach suggested in the rivaling answer!

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You can use itoa() function to convert your integer value to a string.

Here is an example:

int num = 321;
char snum[5];

// convert 123 to string [buf]
itoa(num, snum, 10);

// print our string
printf("%s\n", snum);

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If you want to output your structure into a file there is no need to convert any value beforehand. You can just use the printf format specification to indicate how to output your values and use any of the operators from printf family to output your data.