read in 1000 numbers at once

i have the following code

Code:

---

#include <stdio.h>
#include <stdlib.h>

int main()
{
    char buff[1001];

    fgets(buff, sizeof(buff), stdin);
    printf("\n999th character is %c and the 1000th chacter is %c\n the whole thing = %s\n", buff[999], buff[1000], buff);
    return 0;
}

---

but when i paste in the string of 1000 numbers it just quits doesn't do anything ie the printf doesn't run if i force it to pause with a break point and step past the printf i get the wrong result buff[999] is a space and 1000 is 0

is this doing somthing wierd like trying to convert the integer to a ascii code

The 999th character is at offset 998. The offset 1000 is always '\0'. Take a look:

Code:

---

#include <stdio.h>

int main( void )
{
  char buff[11];

  fgets( buff, sizeof buff, stdin );
  printf( "%s\n", buff );
}

---

Code:

---

$ gcc -g -o test test.c
$ gdb -q ./test
Reading symbols from test...done.
(gdb) l
1    #include <stdio.h>
2   
3    int main( void )
4    {
5      char buff[11];
6     
7      fgets( buff, sizeof buff, stdin );
8      printf( "%s\n", buff );
9    }
(gdb) b 7
Breakpoint 1 at 0x751: file test.c, line 7.
(gdb) r
Starting program: .../test

Breakpoint 1, main () at test.c:7
7      fgets( buff, sizeof buff, stdin );
(gdb) n
1234567890
8      printf( "%s\n", buff );
(gdb) x/11c buff
0x7fffffffda3d:    49 '1'    50 '2'    51 '3'    52 '4'    53 '5'    54 '6'    55 '7'    56 '8'
0x7fffffffda45:    57 '9'    48 '0'    0 '\000'
(gdb)

---

god knows what is going on here..... it says that the max number achievable by multiplying 4 adjacent numbers is 6561 (wrong answer) then says that is achieved by multiplying 7, 3, 1 and 6 together (no where near) on stepping through the inner for loop it seems to think there are 4 9's together (there aren't)

Code:

---

#include <stdio.h>
#include <stdlib.h>

int ascii_to_num(int x);

int main()
{
    int i, j, x, a , b;
    long int answer = 0, temp_answer = 1; //temp_answer has to be 1 rather than 0 as anything * 0 is 0
    char buff[1001];

    fgets(buff, sizeof(buff), stdin);// get the whole number as a string
    for (i = 0, j = 3; j < 1000; i++, j++)
    {
        for (x = i; x < j + 1; x++) // get the four digits between i and j
        {
            temp_answer *= ascii_to_num(buff[x]);
        }
        if (temp_answer > answer)
        {
            answer = temp_answer;
            a = i;
            b = j;
        }
        temp_answer = 0;
    }

    printf("the largest product produced by 4 adjancent numbers is %ld\nthis is produced with the numbers ", answer);
    for (i = a; i < b + 1; i++)
    {
        printf("%c ", buff[i]);
    }
    printf("\n");

    return 0;
}

int ascii_to_num(int x)
{
    int result;

    switch (x)
    {
        case 48:
            result = 0;
        case 49:
            result =  1;
        case 50:
            result =  2;
        case 51:
            result =  3;
        case 52:
            result =  4;
        case 53:
            result =  5;
        case 54:
            result =  6;
        case 55:
            result =  7;
        case 56:
            result =  8;
        case 57:
            result =  9;
    }
    return result;
}
//7316717653133062491922511967442657474235534919493496983520312774506326239578318016984801869478851843858615607891129494954595017379583319528532088055111254069874715852386305071569329096329522744304355766896648950445244523161731856403098711121722383113622298934233803081353362766142828064444866452387493035890729629049156044077239071381051585930796086670172427121883998797908792274921901699720888093776657273330010533678812202354218097512545405947522435258490771167055601360483958644670632441572215539753697817977846174064955149290862569321978468622482839722413756570560574902614079729686524145351004748216637048440319989000889524345065854122758866688116427171479924442928230863465674813919123162824586178664583591245665294765456828489128831426076900422421902267105562632111110937054421750694165896040807198403850962455444362981230987879927244284909188845801561660979191338754992005240636899125607176060588611646710940507754100225698315520005593572972571636269561882670428252483600823257530420752963450

---

> for (x = i; x < j + 1; x++) // get the four digits between i and j
You're not adding together 4 digits.
j keeps increasing.

Try

Code:

---

for ( i = 0 ; i < 1000-4 ; i++ ) {
  for ( j = 0 ; j < 4 ; j++ ) {
    temp_answer *= ascii_to_num(buff[i+j]);
  }
}

---

> temp_answer = 0;
No, you need to reset it back to 1.
Otherwise all your multiplications end up back at zero.

i changed line 17

Code:

---

temp_answer *= ascii_to_num(buff[x]);

---

to

Code:

---

temp_answer += ascii_to_num(buff[x]);

---

and don't get anywhere near the right answers it thinks 7 + 3 + 1 + 6 = 37 even assuming the above output was generated by multiplying 4 9's together (9*9*9*9) 4 * 9 = 36 not 37

i must of done something seriously wrong here for the maths processor to be out of kilt.
coop

Quote:

---

Originally Posted by Salem

> for (x = i; x < j + 1; x++) // get the four digits between i and j
You're not adding together 4 digits.
j keeps increasing.

Try

Code:

---

for ( i = 0 ; i < 1000-4 ; i++ ) {
  for ( j = 0 ; j < 4 ; j++ ) {
    temp_answer *= ascii_to_num(buff[i+j]);
  }
}

---

> temp_answer = 0;
No, you need to reset it back to 1.
Otherwise all your multiplications end up back at zero.

---

how does j increase with in the inner loop only x increases surely

i = 0 j = 3 (diff of 4)
x = i
buff[x] = buff[i]
x++
buff[x] = buff[i+1]
.....
buff[x] = buff[i+3]
now increment i and j
i++, j++
x = i..........

helps when i change the cases for the switch statement from return value to result = value to put a break in each case label duh!! and resetting temp_answer to 0 when i made a comment on the deceleration about setting it to 1 and why is just beyond duh!!

> for (i = 0, j = 3; j < 1000; i++, j++)
This is why you add together 4,5,6,7,8,9.... consecutive numbers.

> temp_answer *= ascii_to_num(buff[x]);
> temp_answer += ascii_to_num(buff[x]);
What exactly are you trying to solve?

Also, ascii_to_num is simply

Code:

---

int ascii_to_num(int x)
{
    return x - '0';
}

---

The standard guarantees that '0' through '9' are consecutive.

i was just trying to make sure the return of the function was correct rather than getting a big number by 9 ^ 4 expecting 36 is easier to work out in my head

im obviously missing a fundimental thing here
[code]
for (i = 0, j = 3; j < 1000; i ++, j++)
for (x = i; x < j +1; x++)
i = 0 j = 3 x = 0
buff[x]
x++
buff[x]
x++
buff[x]
x++
buff[x]
x++ wait x = j + 1 break inner loop
i++ j++
i = 1 j = 4 x = 1
.....

a simple example of what i am trying to achieve with the for loops

Code:

---

#include <stdio.h>
#include <stdlib.h>

int main()
{
    int i, j, k;

    for (i = 0, j = 3; j < 7; i++, j++)
    {
        for (k = i; k < j + 1; k++)
        {
            printf("i = %d j = %d k = %d\n", i, j, k);
        }
        printf("\n");
    }
    return 0;
}

---

produces the output

Code:

---

i = 0 j = 3 k = 0
i = 0 j = 3 k = 1
i = 0 j = 3 k = 2
i = 0 j = 3 k = 3

i = 1 j = 4 k = 1
i = 1 j = 4 k = 2
i = 1 j = 4 k = 3
i = 1 j = 4 k = 4

i = 2 j = 5 k = 2
i = 2 j = 5 k = 3
i = 2 j = 5 k = 4
i = 2 j = 5 k = 5

i = 3 j = 6 k = 3
i = 3 j = 6 k = 4
i = 3 j = 6 k = 5
i = 3 j = 6 k = 6

---

ie i and j stay the same while k loops through the numbers from i to j

OK, so use that to make your loop in the original program.

umm its what i have except i use x rather than k

OK, so instead of reading 1000 chars from a file, test with

Code:

---

char buff[] = "7316717653133";
int n = strlen(buff);
for (i = 0, j = 3; j < n; i++, j++) {
  // etc
}

---

Pick some short example string you can easily verify either on paper, or from just studying the debug.