else 语句在 C 中有效

Question

I'm trying to work out Babbage's difference machine in C. I wrote all the basic idea of the concept: If you are about to find square of 10, for example, first you have to find square of integers before 10. This is how Babbage's machine works. So in my program we have a list of integers and we assume that we already squares of these integers. Giving this information, it must be capable of working out square of any positive integer, without making any multiplication.

BUT, the code just does not execute the "else" part in if-else statements. However, when I deleted everything in "else" statement and simply wrote a printf function, it supplied the conditions well.

So something must be wrong in the else statement, am I doing appending items to array wrong? Is it not allowed to write for loops in If-Else statement in C? I wrote the same algorithm in python and it works well!

ps: I already tried to write a do-while instead of "else" part.

please help, thanks in advance

#include<stdio.h>

int main(){
int integers[] = {0,1,2};
int sq_of_integers[] = {0,1,4};
int first_differences[] = {1,3};
int second_difference[] = {2};
int input;
int i;
int x;
int end2 = 2;
int end1 = 1;

for ( i = 0 ; i<=2 ; i++){
    printf("Enter a number to be squared: ");
    scanf(" %d", &input);

    if (input <= integers[end2]){
        printf("It is already known, sir.\n");
    }else{
        for( x = 0 ; x<= input - integers[-1] ; x++){

            // Calculation of the square root:
            integers[end2+1] = integers[end2]+1;
            sq_of_integers[end2+1] = second_difference[0] + first_differences[end1] + sq_of_integers[end2];
            first_differences[end1+1] = sq_of_integers[end2] +sq_of_integers[-2];
            printf(sq_of_integers[end2]);
            end2 = end2 + 1;
            end1 = end1 + 1;
        }
    }
}
return 0;
}

Answer 1

input - integers[-1] has undefined value. Probably it was negative and so you exit the for loop without processing it once.

Edit: Complete review of code. Please ask if you don't understand something.

You were trying to use printf() without a format argument, probably you compile without warnings. Try to use the command I give to compile.

There was also an index error in your calculation of first_differences values.

small.c:

/*
Compile with MinGW for Windows:
gcc -Wall -Wextra -Werror -std=gnu99 -o small.exe small.c

Compile with linux gcc:
gcc -Wall -Wextra -Werror -std=gnu99 -o small small.c
*/

#define N_UPPER_LIMIT 1023

#include <stdio.h>

int main()
{
    long integers[N_UPPER_LIMIT + 1] = {0, 1, 2};
    long sq_of_integers[N_UPPER_LIMIT + 1] = {0, 1, 4};
    long first_differences[N_UPPER_LIMIT] = {1, 3};
    long second_difference[] = {2};
    int end1 = 1;
    int end2 = 2;

    for (int i = 0; i < 2; i++)
    {
        int input;

        printf("Enter a number to be squared: ");
        fflush(stdout);
        scanf(" %d", &input);

        if (input < 0)
        {
            printf("It is negative, sir.\n");
        }
        else if (input <= integers[end2])
        {
            printf("It is already known, sir.\n");
            printf("square(%ld) = %ld\n", integers[input], sq_of_integers[input]);
        }
        else if (input > N_UPPER_LIMIT)
        {
            printf("Please do not go further than %d, sir.\n", N_UPPER_LIMIT);
        }
        else
        {
            while (input > integers[end2])
            {
                // Calculation of the square root:
                integers[end2 + 1] = integers[end2] + 1;
                sq_of_integers[end2 + 1] = second_difference[0]
                    + first_differences[end1] + sq_of_integers[end2];
                first_differences[end1 + 1] = sq_of_integers[end2 + 1]
                    - sq_of_integers[end2];
                end2++;
                end1++;
                printf("square(%ld) = %ld\n", integers[end2], sq_of_integers[end2]);
            }
        }
    }

    return 0;
}

It could be a good exercise to get rid of the static limit. If you want to do so, you will have to allocate memory for your variables with malloc() , and either put a limit as a program argument, or try to change the size allocated with calls to aither malloc() of realloc() .