I want to calculate the sum of input numbers using pointer concept in c language.But when i compile the given below program correct value for sum does not appear. help me to find the mistake i have done in the below program.
#include<stdio.h>
void main()
{
int g , *p;
int sum = 0;
int x=1;
for(int i=1; i<3; i++ )
{
scanf("%d ", &g);
}
p = &g;
while( x < 3){
sum = sum + *p;
p++;
x++;
}
printf("\n sum = %d ",sum);
}
Your g is only one integer so:
Each time you call scanf("%d ", &g);, you will overwrite the previous value.
When you increment the pointer in p++;, that pointer will no longer be valid. (Where do you think it will point to?)
If you want to store three different values in g, you need to make it an array of integers.
To do this, make the following changes to your code:
int g[3] , *p; // "g" can now store three different values
int x=0; // Later on - counting from 0 thru 2 in the "while" loop
//...
for (int i=0; i<3; i++) // NOTE: Arrays begin at "0" in C!
{
scanf("%d ", &g[i]); // Store to the element indexed by "i"
}
//...
p = g; // For arrays, don't need the & operator: this will give address of first element
You can store only one number in g.
Therefore, p++; here will make p point at an invalid place.
You should allocate an array to store all input values.
Also note that you should use standard int main(void) in hosted environment instead of void main(), which is illegal in C89 and implementation-defined in C99 or later, unless you have some special reason to use non-standard signature.
#include<stdio.h>
int main(void)
{
int g[3] , *p;
int sum = 0;
int x=1;
for(int i=1; i<3; i++ )
{
scanf("%d ", &g[i]);
}
p = &g[1];
while( x < 3){
sum = sum + *p;
p++;
x++;
}
printf("\n sum = %d ",sum);
}
Related
I'm trying to create a program which randomly decides how many cards you have, then randomly allocates a value to each of those cards.
I have managed to randomise the amount of cards, and I know how to randomise their values using an array and a for loop, but the problem is that this method only works when I manually choose a value for the number of elements in the array, but I want the number of elements to be the random amount of cards.
How do I go about this?
Here's my code so far to show what I mean. And yes, I'm aware the code probably could be done better but this is my first C assignment and I'm a complete beginner.
Thanks :)
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <windows.h>
int main(void)
{
system("cls"); /* Clears output to start */
srand(time(NULL)); /* Sets seed for random number generator */
int player1_amount = rand() %9 + 2; /*Generates random number for player 1's amount of cards */
int player2_amount = rand() %9 + 2; /*Generates random number for player 2's amount of cards */
int a = 1; /* For loop purposes */
while(a <= 1) /* While loop to print out each player's amount of cards once */
{
printf("Player 1 you have %d cards! \n", player1_amount);
Sleep(500);
printf("Player 2 you have %d cards! \n", player2_amount);
a++;
}
Sleep(1000); /* Delays for 1 second before printing card values */
int values[3]; /* Creates an array with 3 elements, but I want the number of elements to be player1_amount from above */
int b; /* Random variable for the loop */
int size = sizeof(values) / sizeof(values[0]); /* Gets length of array */
for (b = 0; b < size; b++) /* For loop randomises 3 values and then stops */
{
values[b] = rand() % 10 +1;
}
printf("Player 1 your cards are"); /* For loop to print out the values one after the other */
for(b = 0; b < size; b++)
{
printf(" %d, ", values[b]);
}
getch();
return 0;
}
I believe you will want to use malloc or calloc for that with a pointer.
int *values = (int *)calloc(player1_amount, sizeof(int));
Just make sure you free your allocation when done:
free(values);
C allows you to declare variable sized array. If you are not interested in using functions like malloc or calloc you can simply use variable to declare array as I've done here :
#include <stdio.h>
void main()
{
int x;
printf("\nEnter the value of x : ");
scanf("%d" , &x);
int array[x];
for(i = 0 ; i < x ; i++)
{
printf("Enter the element : ");
scanf("%d" , &array[i]);
}
for(i = 0 ; i < x ; i++)
{
printf("%d " , array[i]);
}
}
This program runs correctly without any error. So your problem is solved here itself without using malloc or calloc. But just make sure you declare your array after scanning or giving value to your variable which will represent the size of your array(here : x is the variable) and in your case I guess : player1_amount.
But still if you want to use malloc then here it goes :
#include <stdio.h>
#include <stdlib.h>
void main()
{
int x , i;
int * array;
printf("\nEnter the value of x : ");
scanf("%d" , &x);
array = (int *) malloc(x * sizeof(int));
for(i = 0 ; i < x ; i++)
{
printf("Enter the element : ");
scanf("%d" , &array[i]);
}
for(i = 0 ; i < x ; i++)
{
printf("%d " , array[i]);
}
}
Both the codes will give you same output.
A little explanation ...
Malloc will take input parameter as the amount of memory you wish to allocate to given variable(like 'array' in our case) in bytes and will output the pointer to that block of memory.
Since here we are working with integer array the return type is cast as : (int *), had it been a character array we would type cast it as : (char *).
I am trying to create a simple program where the user will have to enter a series of numbers and the program should output the square and the cube of the given number. However, when I try to use an array, it prints some random numbers I didn't even input. Any help would be appreciated to eliminate the unecessary input. Thank you.
#include <stdio.h>
int main()
{
char *value;
value = malloc(sizeof(20));
float answer;
int x;
int y;
scanf("%s" , value);
for(x=0; x < 20; x++)
{
y = value[x] - '0';
printf("\nThe square of %d is: %d" , y , y*y);
printf("\nThe cube of %d is: %d \n" , y , y*y*y);
}
return 0;
}
You are taking input in char and doing arithmetic operations on it.
Use this code, it will give you correct output.
#include <stdio.h>
int main()
{
int *value;
value = (int *)malloc(20 * sizeof(int));
//float answer;
int x;
int y;
for(x=0; x < 20; x++)
{
scanf("%d" , value + i);
}
for(x=0; x < 20; x++)
{
y = value[x];
printf("\nThe square of %d is: %d" , y , y*y);
printf("\nThe cube of %d is: %d \n" , y , y*y*y);
}
return 0;
}
The problem is with your malloc statement.
sizeof is used to determine the parameter size - in your case a hard-coded integer. The generated array is of size 4, which is exactly sizeof(20) instead of 20 integers which is 20*sizeof(int). It will be best to allocate the array statically if you know what size you need, see code below:
#include <stdio.h>
int main()
{
// This line sets value to an array of 20 ints
int value[20];
// Another, less favorable option, but still works:
// char *value = malloc(20 * sizeof(int))
float answer;
int x;
int y;
scanf("%s" , value);
for(x=0; x < 20; x++)
{
y = value[x] - '0';
printf("\nThe square of %d is: %d" , y , y*y);
printf("\nThe cube of %d is: %d \n" , y , y*y*y);
}
return 0;
}
The expression sizeof(20) returns the size of an int (the literal 20 is an int), which is typically only 4 bytes. In other words, you are only allocating a single integer for your array. All access outside of that single integer will result in undefined behavior.
You need to allocate sizeof(int) times the number of elements, if you want to dynamically allocate the memory. Or (which I recommend) use a normal array:
int value[20];
There is also another problem, in that you only read a single value from the user. You should probably be reading in the loop too.
But if you read in the loop, then there is really no need to even have an array to begin with, only a single int Variable which you read into, and then print its value as squared and cubed.
So the code could be simplified as
#include <stdio.h>
int main(void)
{
int value;
for (unsigned i = 0; i < 20 && scanf("%d", &value) == 1; ++i)
{
printf("The square of %d is: %d\n", value, value * value);
printf("The cube of %d is: %d\n", value, value * value * value);
}
return 0;
}
You also need to be careful of overflows when multiplying.
I am having difficulties initializing an array to how values given from a for loop, I want to discard the prime numbers calculated and then keep the non prime numbers in an array, which the size of the array must be unknown from the beginning. I must then call collect the numbers from the array and then apply the Carmichael equation to them to find Carmichael numbers.
Applying the equation to the values in the array is what I am finding difficult as well.
This is my code:
int main(int argc, char **argv){
int a ,b;
int notPrime[] = {};
printf("Type in two non negative intergers: \n");
scanf("%d" "%d", &a , &b);
int i=a , k=0 ,count=0, j, p, m;
for (i < b;){ //from the integers given b must be the larger of the two
if (i==0 || i==1) { //to calculte the prime numbers
notPrime[k]=i;
}else{
for( j=2;j<i;j++){
if(i%j==0){
break;
}else{
notPrime[k]=i;
}
}
}
i++;
k++;
}
p=0;
if (p<=k){
for (m=1;m<notPrime[p];m++){
if((pow(m,notPrime[p])-m)%notPrime[p]==0){ //use of the values in the array and use of the carmichael equation
count=count+1;
}
if(count==notPrime[p]-1){
Printf( "%d \n", ¬Prime[p]) ;
}
}
}
return 0;
}
i have errors on for (i < b;){, if((pow(m,notPrime[p])-m)%notPrime[p]==0){ and finally the print statment Printf( "%d \n", ¬Prime[p])
Please could I get a little help, just set me in the right direction and I will try to correct.
xRapture
for (i < b;){
This is not a valid syntax for for loop . You can write like this instead -
for (;i < b;){
And this -
if((pow(m,notPrime[p])-m)%notPrime[p]==0){ //
pow return double and notPrime[p] is int . % operator on double and int .
Explicitly cast result of pow to int.
Also this -
printf( "%d \n", ¬Prime[p]) ;
^ this is not needed
don't pass address of int.
Edit -
You can declare your array as this after taking input a and b -
int notPrime[a] = {0}; // or size b as you desire
I'm trying to calculate the size of the file . The process I've followed is to read the file and store it in an array and calculate its size. However,I really don't know ... I tried n number of ways..I've to pass this size as an attribute to the frequency function.along with the name of the array.
#include <stdio.h>
#include<conio.h>
void frequency (int theArray [ ], int ??????, int x)
{
int count = 0;
int u;
for (u = 0; u < ??????; u++)
{
if ( theArray[u]==x)
{
count = count + 1 ;
/*printf("\n%d",theArray[u]);*/
}
else
{
count = count ;
}
}
printf ("\nThe frequency of %d in your array is %d ",x,count);
}
void main()
{
FILE*file = fopen("num.txt","r");
int integers[100];
int i=0;
int r = 0;
int num;
int theArray[100];
int there[100];
int n;
int g;
int x;
while(fscanf(file,"%d",&num)>0)
{
integers[i]=num;
printf("\n%d",(integers[i]));
there[r] = integers[i];
i++;
}
//printf("%d",there[r]);
//printf("\n%d",file);
//fclose(file);
printf ("\n OK, Thanks! Now What Number Do You Want To Search For Frequency In Your Array? ");
scanf("\n%d", &x);/*Stores Number To Search For Frequency*/
frequency(integers,????????,x);
getch();
fclose(file);
}
?????? is the size of the integer array from where i read the file and stored it.
I could not find a way to calculate the size of the array into which i copied my file. My idea is to calculate the frequency of a number in that file and calculate the probability of it's occurrence and thereby calculating entropy..Suggestions please!
I don't know why you are initializing so many variables and some of them with awkward names like ??????.
Your main problem is that the call to function should be
frequency(integers, i, x);
Your code with the awkward irrelevant parts removed will look like
#include <stdio.h>
#include<conio.h>
void frequency (int theArray [ ], int number, int x)
{
int count = 0;
int u;
for (u = 0; u < number; u++)
{
if ( theArray[u]==x)
count++;
}
printf ("\nThe frequency of %d in your array is %d ",x,count);
}
void main()
{
FILE*file = fopen("num.txt","r");
int integers[100];
int i=0;
int num;
int x;
while(fscanf(file,"%d",&num)>0)
{
integers[i]=num;
printf("\n%d",integers[i]);
i++;
}
printf ("\n OK, Thanks! Now What Number Do You Want To Search For Frequency In Your Array? ");
scanf(" %d", &x);/*Stores Number To Search For Frequency*/
frequency(integers,i,x);
getch();
fclose(file);
}
There are a lot of parts of this code that don't make sense, but I assume it is your debugging trying to figure out what is wrong. The answer to your specific question is:
For each value read from the file you set integers[i] to the value and then increment i. Thus i is the count of items in integers. You then pass integers to frequency(), so i should be passed to the second parameter as the count.
Note that if there are more than 100 values in the file, you will over index integers and cause unpredictable behavior.
To calculate length of array:
int len= sizeof(arr)/sizeof(arr[0]);
It will give length of array without looping.
My program is supposed to order a list of numbers inputed by the user, but it crashes even before reaching the first printf. My compiler makes 2 warnings, but I don't see the issue. I haven't studied pointers yet, so I didn't want to use them. Here are the messages:
In function `selection_sort':
[Warning] passing arg 2 of `selection_sort' makes pointer from integer without a cast
In function `main':
[Warning] passing arg 2 of `selection_sort' makes pointer from integer without a cast
.
#include<stdio.h>
int selection_sort(int n, int v[n])
{
int high = v[0];
int i;
for(i = 0; i < n; i++)
high = high < v[i]? v[i] : high;
if(n - 1 == 0)
return;
v[n - 1] = high;
n -= 1;
selection_sort(n, v[n]);
}
int main(void)
{
int n, i;
int v[n];
printf("Enter how many numbers are to be sorted: ");
scanf("%d", &n);
printf("Enter numbers to be sorted: ");
for(i = 0; i < n; i++)
scanf("%d", &v[i]);
selection_sort(n, v[n]);
printf("In crescent order: ");
for(i = 0; i < n; i++)
printf("%d ", v[i]);
getch();
return 0;
}
Your program is using a variable length array, a feature that was added in C99.
However, you declare its size based on an uninitialized variable. What did you believe would happen there?
In C, variables declared inside functions are NOT set to 0. They are not set to anything. They pick up whatever value was left on the stack or in the register that they are assigned.
I believe that your program is crashing because n in int v[n] is a ridiculously big number and v is trying to use too much memory.
You can probably fix this by moving your array declaration below the scanf that reads in n.
You need to pass v, not v[n] to the function selection_sort. v is the array, v[n] is actually an out of bounds element of v.
the line should be selection_sort(n, v);