CODEWITHSUNDEEP
c++string
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Reputation: 57

How to solve error "invalid conversion of char to char*" when using strupr and strlwr?

#include <iostream>
#include <cstring>
using namespace std;

int main()
{
    int i;
    char s[100];
    cin >> s;
    for(i=0;i<strlen(s);i++)
    {
        if(islower(s[i])==1)
        {
            s[i]=strupr(s[i]);
            cout << s[i];
        }
        else
        {
            s[i]=strlwr(s[i]);
            cout << s[i];
        }
    }
    return 0;
}

These two lines i.e. s[i]=strupr(s[i]) and s[i]=strlwr(s[i]) shows this error :

invalid conversion from char to char*.

How can I solve it? Thank you.

Upvotes: 0

Views: 662

Answers (4)

Jonas
Jonas

Reputation: 7017

You should use these two instead:

s[i] = std::toupper(s[i]);
s[i] = std::tolower(s[i]);

Remember to include <cctype>. Here is a link to some documentation of std::toupper and std::tolower.

The problem is that strupr and strlwr work on entire strings, not single characters. Moreover, they operate in-place and they are non standard.

Side note:

You could consider using a std::string s instead of char s[100], this removes the current overflow opportunity in cin >> s;.

Update:

It is possible to use std::transform like so:

std::transform(std::begin(s), std::end(s), std::begin(s), [] (char c) { return std::islower(c) ? std::toupper(c) : std::tolower(c); });

One benefit of using std::begin(s) and std::end(s) is that it works for both std::string, std::vector and even char[100].

Upvotes: 7

const_ref
const_ref

Reputation: 4096

strupr and strlwr expect a char* and not a char as their parameter.

You would need to pass the whole s array instead of s[i]

Alternatively use the std::toupper and std::tolower which would allow you to do each character in turn.

You can also get rid of the raw loop by using std::transform and a predicate or lamda

char InvertCase(char c)
{
    return islower(c) ? std::toupper(c) : std::tolower(c);
}

std::transform(s.begin(), s.end(), back_inserter(result), InvertCase);

Upvotes: 3

AlexP
AlexP

Reputation: 4430

strupr() modifies in place its string (that is, char[]) argument replacing all lowercase letters with uppercase. I think that you are confusing strupr() with toupper().

Note that by using strupr() or toupper() you are making an implicit assumption that each char represents a character; this is not true for multi-byte encodings such as UTF-8.

Upvotes: 2

djgandy
djgandy

Reputation: 1135

sdtrupr and strlwr take char * as an argument. To convert a single character use tolower and toupper

Upvotes: 2

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