# help for my cuda code 

**URL:** <https://forums.developer.nvidia.com/t/help-for-my-cuda-code/35284>\
**Category:** Teaching & Curriculum Support\
**Created:** [October 22, 2014, 3:47pm UTC](https://forums.developer.nvidia.com/t/help-for-my-cuda-code/35284 "2014-10-22T15:47:27Z")\
**Posts on this page:** 3\
**Page:** 1

<div class="post-metadata">

**Author:** ![medmab](https://sea2.discourse-cdn.com/nvidia/user_avatar/forums.developer.nvidia.com/medmab/32/10557_2.png) [@medmab](https://forums.developer.nvidia.com/u/medmab)\
**Post date:** [October 22, 2014, 3:47pm UTC](https://forums.developer.nvidia.com/t/help-for-my-cuda-code/35284/1 "2014-10-22T15:47:27Z")

</div>

Hello.

I’m new in cuda programing and I’m trying to write code for CUDA “addition two vectors” .but I met a problem. if you can help me. this is the code .

#include “cuda\_runtime.h”  
#include “device\_launch\_parameters.h”

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

**global** void vecAdd(int \*a, int \*b, int \*c, int n)  
{  
// Get our global thread ID  
int id = threadIdx.x;

```
// Make sure we do not go out of bounds
if (id < n)
	c[id] = a[id] + b[id];

```

}

#define N 8

void random\_ints(int\* a, int h)  
{

}

int main(void){

```
int *a, *b, *c;
int *d_a, *d_b, *d_c;
int size = N*sizeof(int);

//aloueé l'espace pour les copie de a,b etc dans le device (gpu)
cudaMalloc((void**)& d_a, size);
cudaMalloc((void**)& d_b, size);
cudaMalloc((void**)& d_c, size);

//aloueé de l'espace des copies de a,b et c dans le host (cpu) et affecter les variables
a = (int *)malloc(size);random_ints(a, N);
b = (int*)malloc(size); random_ints(b, N);
c = (int*)malloc(size);

for (int i = 0; i < size; ++i)
{
	a[i] = i;
	b[i] = i;
	c[i] = 0;
}

vecAdd(a, b, c,N);

//copier les affectation dans device (gpu)
cudaMemcpy(d_a, a, size, cudaMemcpyHostToDevice);
cudaMemcpy(d_a, b, size, cudaMemcpyHostToDevice);

//executer add() kernel dans le GPU avec N threads

vecAdd <<< 1, N >>> (d_a, d_b, d_c); // problem here

//copier le resultat du gpu
cudaMemcpy(c, d_c, size, cudaMemcpyDeviceToHost);

free(a); free(b); free(c);
cudaFree(d_a); cudaFree(d_b); cudaFree(d_c);

printf("\nPress any key to exit...");
char w;
scanf("%w", &w);

return 0;

```

}

---

<div class="post-metadata">

**Author:** ![Skybuck](https://sea2.discourse-cdn.com/nvidia/user_avatar/forums.developer.nvidia.com/skybuck/32/9717_2.png) [@Skybuck](https://forums.developer.nvidia.com/u/Skybuck)\
**Post date:** [March 31, 2015, 1:39am UTC](https://forums.developer.nvidia.com/t/help-for-my-cuda-code/35284/2 "2015-03-31T01:39:51Z")

</div>

What’s the problem ? :)

---

<div class="post-metadata">

**Author:** ![mrjokero](https://developer.download.nvidia.com/images/forums/profile-default-devtalk-84.png) [@mrjokero](https://forums.developer.nvidia.com/u/mrjokero)\
**Post date:** [March 31, 2015, 7:24pm UTC](https://forums.developer.nvidia.com/t/help-for-my-cuda-code/35284/3 "2015-03-31T19:24:34Z")

</div>

To at least compile you should remove the call to vecAdd(a, b, c, N); as by that name you only defined a kernel function. Here you try to call a host function.

Your kernel function **global** void vecAdd(int \*a, int \*b, int \*c, int n) accepts 4 arguments and you called it with only 3 in vecAdd \<\<\< 1, N \>\>\> (d\_a, d\_b, d\_c); As you already noticed you should call it with the last argument of size which is N. The call will look like this:  
vecAdd \<\<\< 1, N \>\>\> (d\_a, d\_b, d\_c, N);

The code should now compile.

Some errors in code:

When you iterate over all elements of host array in a for loop, the array index ‘i’ should be less than number of elements (N in your code) when you start from 0. In the conditional statement you check against size, which is size in bytes of these arrays. The for loop should look like this:  
for (int i = 0; i \< N; ++i)

The second cudaMemcpy copies from host b array to device d\_a array again. You probably wanted to coby the host array b to device array d\_b like this:  
cudaMemcpy(d\_b, b, size, cudaMemcpyHostToDevice);

Hope that helps.