Prefix Suffix Substring in C

#include <bits/stdc++.h>

int main()
{
    // Variable declaration and initialization
    int i = 0;
    bool flag = false;
    int length = 0;
    char str[100];

    // Take input from user
    fgets(str, 100, stdin);

    // Prefix matching
    if (str[0] == 'a' && str[1] == 'b')
    {
        printf("Prefix matched");
    }
    else
    {
        printf("Prefix not matched");
    }

    printf("\n\n");

    // Suffix matching
    length = strlen(str)-1;

    if (str[length - 2] == 'a' && str[length - 1] == 'b')
    {
        printf("Suffix matched");
    }
    else
    {
        printf("Suffix not matched");
    }

    printf("\n\n");

    // Substring matching
    for (i = 0; i < length; i++)
    {
        if (str[i] == 'a' && str[i + 1] == 'b')
        {
            flag = true;
            break;
        }
    }

    if (flag)
    {
        printf("Substring matched");
    }
    else
    {
        printf("Substring not matched");
    }

    return 0;
}