Driver code
public static void Main ( ) { string s1 = " for " ; string s2 = " geeksforgeeks " ; int res = isSubstring ( s1 , s2 ) ; if ( res == - 1 ) Console . Write ( " Not ▁ present " ) ; else Console . Write ( " Present ▁ at ▁ index ▁ " + res ) ; } }