CODEWITHSUNDEEP
c
yesmina waah
yesmina waah

Reputation: 31

Cannot convert parameter 1 from char to const char for strcmp

I just started using pointers in c. I thought to sort a string by entering the string in the command prompt.

When I try to implement it, I get this error: 

'strcmp' : cannot convert parameter 1 from 'char' to 'const char *'

Could you please guide me and tell me how to make the code with less pointer and more of array?

char *sort(char *sortIt)
{
    char *p =sortIt;
    //p = (char*)calloc(sizeof(char));
    char temp[3];
    int len = strlen(sortIt);
    for(int i=0;i<len;i++)
    {
        for(int j=i+1;j<len;j++)
        {
            if(strcmp(p[i],p[j])>0)
            {
                strcpy(temp,p[i]);
                strcpy(p[i],p[j]);
                strcpy(p[j],temp);
            }
        }
    }

    for(int ij=0;ij<len;ij++)
      printf("%s", p[ij]);
}

int main(char argc, char **argv)
{
    char *p=argv[1];

    sort(p);
}

Upvotes: 0

Views: 5191

Answers (3)

chux
chux

Reputation: 153348

It appear code is attempting to sort the char in a string. Corrections and ideas noted in code.

char *sort(char *sortIt)
{
    // After assignment p & sortIt never change. Only need one of these.
    char *p =sortIt;
    // casting the return of callloc() and malloc() is frowned upon.
    // Note: sizeof(char) is _always_ 1
    //p = (char*)calloc(sizeof(char)); 
    char temp[3];  // Only 1 char is needed.  Best to declare in inner lock
    int len = strlen(sortIt);  // Better to use size_t len,i,j,ij;
    for(int i=0;i<len;i++)
    {
        for(int j=i+1;j<len;j++)
        {
            // Only need to compare p[i] > p[j]
            if(strcmp(p[i],p[j])>0)
            {
                // Only need to swap  p[i] p[j]
                strcpy(temp,p[i]);
                strcpy(p[i],p[j]);
                strcpy(p[j],temp);
            }
        }
    }
    // Only need to print the string once
    for(int ij=0;ij<len;ij++)
      printf("%s", p[ij]);
// missing return
}

Sample solution:

char *sort(char *p) {
  size_t len = strlen(p);
  for (size_t i = 1; i < len; i++) {
    for (size_t j = 0; j < i; j++) {
      /// As this code changed the order of indexing, maybe p[i] < p[j]
      if (p[i] > p[j]) { 
        char temp;
        temp = p[i];
        p[i] = p[j];
        p[j] = temp;
      }
    }
  }
  printf("%s\n", p);  // Recommend adding \n
  return p;
}

[Edit]

I see trouble with the original main() code. Below is code with suggested changes: 

int main(char argc, char **argv)
{
    // Good to test if argv[1] is valid.
    if (argc <= 1) return 1;
    // Although legal for historic reasons, best to 
    // char *p=argv[1];  
    const char *p=argv[1]; 
    // Since sort() is going to re-arrange p, either sort() allocates new memory
    //   or we allocate memory here.  Then const char *p is not needed.
    size_t size = strlen(argv[1]) + 1;
    char *q;
    q = malloc(size);
    memcpy(q, argv[1], size);
    // sort(p);
    sort(q);
    // Good policy to free allocated memory
    free(q);
    return 0;  // Always good to return a value from main()
}

Upvotes: 0

NV Bhargava
NV Bhargava

Reputation: 373

EDIT:

Change all the 

 p[i], p[j]

to

 &p[i], &p[j]

because you want the const char pointers. In your original case, you will be just looking at chars.

Upvotes: 0

CS Pei
CS Pei

Reputation: 11047

In C, strings mean null terminated strings. Therefore most C library functions take advantage of that. For example, strcmp, strcpy, etc.

So your code is wrong in calling strcmp(p[i],p[j]) and strcpy(temp,p[i]) because strcmp and strcpy deal with strings not chars and p[i] is a char.

To compare chars in C, you can just use if (p[i] > p[j]) .... And for copy a char you can just char c = p[j];.

Upvotes: 1

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