How can one convert an int to a char in C?

I believe the example you provided should work as you would expect. Most of it is unnecessary though. Adding 3 to an element on 3rd index is as simple as: #include <stdio.h> int main() { char str[] = "10000"; str[3] += 3; printf("%s\n", str); return 0; } But keep in mind that when number on 3rd index is larger than 6, you'll get garbage instead of sensible output.

Use "itoa" function. char *  itoa ( int value, char * str, int base ); value : Value to be converted to a string. str: Array in memory where to store the resulting null-terminated string. base: Numerical base used to represent the value as a string, between 2 and 36, where 10 means decimal base, 16 hexadecimal, 8 octal, and 2 binary. It should work for you.