Level of Nested for loop in c+

[mrityunjay23]

I have written a c program with 256 nested for loop. But, I have heard that it is not possible to run this program in C. But, I have also heard that we can run a C++ program with 256 nested for loop. I have converted this C Program in to C++ by adding iostream header and I have changed printf to cout statement.

After adding suitable c header files, Can I able to use string functions: strlen, strcat; file functions fopen, fclose, fgets; memory functions: free and malloc in same way as we use in C.

[helios]

Why do you need that many levels of nesting? What are you trying to do?
Any series of nested loops can be converted into a recursive function:

#define N 256

void useful_function(int variables[N]);

void nesting(int current_level, int variables[N], int limits[N]){
    if (!current_level){
        useful_function(variables);
        return;
    }

    int *i = variables + current_level - 1;
    int n = limits[current_level - 1];
    for (*i = 0; *i < n; ++*i){
        nesting(current_level - 1, variables, limits);
    }
}

int main(){
    int variables[N];
    int limits[N];
    //Note: limits[0] is the limit for the deepest level of nesting.
    limits[0] = 10;
    limits[1] = 42;
    //etc.
    nesting(N, variables, limits);
    return 0;
}

As far as I know, there's nothing in C or C++ that forbids nesting loops arbitrarily deep (until you run out of stack space for all the variables). And yes, you can use standard C functions from C++.

[JLBorges]

> I have written a c program with 256 nested for loop.

This is fundamentally wrong, unless you were doing it for purposes of testing the implementation of a compiler. Consider using a different algorithm (an elegant option would be to write it recursively).


> I have also heard that we can run a C++ program with 256 nested for loop.

The standard does not guarantee it.

Nesting levels of compound statements, iteration control structures, and selection control structures [256].

The bracketed number following each quantity is recommended as the minimum for that quantity. However, these quantities are only guidelines and do not determine compliance.

> I have heard that it is not possible to run this program in C.

You may be able to run such a program in C. Unlike C++, C does impose minimum requirements on implementations; IIRC, C99 requires that an implementation shall be able to translate a program with 127 nesting levels of blocks. This is the lower limit; an implementation may allow deeper levels of nesting, and IIRC the C99 standard suggests that if possible, the implementation should not impose fixed limits.


> After adding suitable c header files, Can I able to use string functions: strlen, strcat;
> file functions fopen, fclose, fgets; memory functions: free and malloc in same way as we use in C.

Yes, C compatibility headers are available. Almost in the same way. For example:

int* p = malloc( 100 * sizof(int) ) ;
double* q = p ;

is valid C, but not valid C++.

Ideally include the standard C++ headers <cstring>, <cstdio> etc. and then use std::strlen, std::fopen etc.

For details, see: http://en.cppreference.com/w/cpp/header