How to create custom filenames in C?

Question

Please see this piece of code:

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

int main() {
    int i = 0;
    FILE *fp;
    for(i = 0; i < 100; i++) {
        fp = fopen("/*what should go here??*/","w");
        //I need to create files with names: file0.txt, file1.txt, file2.txt etc
        //i.e. file{i}.txt
    }
}

Answer 1

for(i = 0; i < 100; i++) {
    char filename[sizeof "file100.txt"];

    sprintf(filename, "file%03d.txt", i);
    fp = fopen(filename,"w");
}