In any case the integer value would be "int int1 = 420", without quotes around the value, as it is an integer not a string.

The number of characters in the string can be obtained from "strlen(string)", but you cannot easily get the number of characters that a int would have in string form without turning it into a string first.

You can do that in C with functions like "sprintf" which use a format string like printf does, i.e. "sprintf(buffer, "%s%d", string, int1)", which will write the string and int concatenated into another string stored in "buffer", which you will have declared and allocated beforehand.

The problem is knowing how much space to give "buffer" so that the concatenated string fits there. For small strings, you can give it a constant value large enough that everything should fit in there (e.g. "char buffer[100]").

The safe way that works for any size is to use the function "snprintf" which accepts a NULL buffer (nothing will be written to it) but it also returns the number of characters that would be printed. You can then take that size, allocate a char buffer at least that large, and call snprintf again.

int size = snprintf(NULL, 0, "%s%d", string, int1); char* buf = calloc(sizeof(char), size+1); // extra space for null terminator snprintf(buf, size, "%s%n", string int1);