Whai is block structure???

C is not a block structure language in Tha sense of Pascal or similar language, because function may not be defined within other function. On the other hand, declarations of variables (including initializations) may follow the left brace that introduce any compound statement, not just the one that begins a function. Variable declared in this way hide any identically named variables in outer blocks, and remain in existence until the matching right brace. For example​, in
If (n > o) {
Int i; /* declare a new i */
For (i = o ; i < n ; i++)
. . .
}