Searching in array of struct in C

Question

How to search on char that has been randomly generated in an array of structures. If char is found the function must return the info[i].num in array of struct, where info is the array of structures (see code below).

I got error in gcc

 warning: comparison between pointer and integer
 if(info[j].name == s );

how can I use correct comparison ??

#include <stdio.h>
#include <stdlib.h>
#include<string.h>
#define InfoSize  3 

int main(int argc, char *argv[]) 
{  
char arr[20];
struct st
{    
    char name[20];  
    int num[5];   
}; 

struct st info[InfoSize] = {{ "some10",6 },{"some50",8},{"some5",4}};

         int r = rand() % (50 + 1 - 10) + 10 ;
         char s = sprintf( arr, "some%d", r );


  for(int j=0;j<3;j++){

     if(info[j].name == s )
     printf("found  %s  and it's num =%d",info[j].name,info[j].num);

}

user3629249 · Accepted Answer · 2017-12-25T19:34:54.770

the following proposed code:

cleanly compiles
incorporated the majority of the comments to the question
performs the desired functionality
documents why each header file is included
the code will probably fail to find a matching entry in the strut array because the generation of the arr[] contents could have been any value from 10 to 50 so will never result in a 5 appended to the string: some. And is unlikely to append a 10 or 50.

And now the proposed code

#include <stdio.h>    // printf(), sprintf()
#include <stdlib.h>   // rand(), srand()
#include <string.h>   // strcmp()
#include <time.h>     // time()


#define INFO_SIZE   3
#define MAX_ARR_LEN 20

int main( void )
{
    char arr[ MAX_ARR_LEN +1 ];

    struct st
    {
        char name[20+1];  // +1 to allow for trailing NUL byte
        int num;
    };

    struct st info[ INFO_SIZE ] =
    {
        { "some10",6 },
        { "some50",8 },
        { "some5",4  }
    };

    srand( (unsigned int)time( NULL ) );
    int r = (rand() % 41) + 10 ;
    sprintf( arr, "some%d", r );


    for(int j=0; j<INFO_SIZE; j++ )
    {
         if( strcmp( info[j].name, arr )  == 0 )
         {
             printf("found  %s  and it's num =%d",info[j].name,info[j].num);
         }
    }
}

score -1 · Answer 2 · answered Dec 25 '17 at 18:43

Your program is missing quite a few things. First order of business is you need to set seed for rand function in order to get pseudo random numbers.

The warning you're getting ( not error, at least on my compiler) tells you you're comparing pointer with integer because an arrays in c are actually plain old pointers.

char s = sprintf( arr, "some%d", r );

According to https://www.tutorialspoint.com/c_standard_library/c_function_sprintf.htm sprintf sends output to your arr variable and retruns a value depending on the success of the operation so the following code:

if(info[j].name == s )

should be written as

if(strcmp(info[j].name,arr)==0)

I suggest you try to grasp core concepts of C as it can be of great help in your future programming life even if you never use C again.

Searching in array of struct in C

2 Answers2