Nesting of functions : In C, each function can contain one or more than one function in it. There is no limit as to how deeply functions can be nested. Consider the following example,
function main(){
function01();
}
function function01(){
function02();
}
function function02(){
//do something more here.
}
In the above example, The main() function contains function01(), the function01() contains function02 and so on. This is nesting of functions.