Check if input is integer or not

#include<stdio.h>
#include<string.h>
#include<stdlib.h>
int main() {
    char inp[100];
    // receive input as string
    scanf(" %s", inp);

    // use strlen function to get the length of the string
    int len = strlen(inp);

    // check if the input is valid by looping through the string from 0 to len-1
    for(int i=0;i<len;i++) {
        // if the character ASCII value is not between 0 and 9, then it is not a digit
        if(inp[i] < '0' || inp[i] > '9') {
            printf("Invalid input\n");
            return 0;
        }
    }

    // if the loop completes without returning, then the input is valid
    // convert the string to integer using atoi function
    int num = atoi(inp);

    // print the integer
    printf("The number is %d\n", num);
}