delete string function in c

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

void deleteString(char *str, int start, int length) {
    int i, j;
    int len = strlen(str);

    for (i = start, j = start + length; j <= len; ++i, ++j) {
        str[i] = str[j];
    }

    str[i] = '\0';
}

int main() {
    char str[] = "This is a sample string.";

    printf("Before deletion: %s\n", str);

    deleteString(str, 5, 4);

    printf("After deletion: %s\n", str);

    return 0;
}