String variable assignment gives pointer error

Question

string reading_lev(int a, int b, int c)
{
    float L = (a / b) * 100;
    float S = (c / b) * 100;
    float index = 0.0588 * L - 0.296 * S - 15.8;
    if (round(index) <= 16 && round(index) >= 1)
    {
        string val = printf("Grade %f", index);
    }
    else if (round(index) > 16)
    {
        string val = printf("Grade 16+");
    }
    else
    {
        string val = printf("Before Grade 1");
    }
    return val
}

The error is in the first if block. There are cs50 libraries involved.

error: incompatible integer to pointer conversion initializing 'string' (aka 'char *') with an expression of type 'int' [-Werror,-Wint-conversion]

string val = printf(...)? printf returns an int, you need to allocate space and then use snprintf to return a string. — David Ranieri
val only exists until the closing brace }, so the return should also be generating an error. — user3386109

Sourav Ghosh Sourav Ghosh · Accepted Answer · 2020-04-08T20:08:10

The error message is self explanatory.

printf() returns an int, you cannot assign it to variable of type char*.

That said, you have multiple other issues:

The return statement uses a block scope variable, which is out of it's scope.
The return statement is missing a ; - syntax error.

To fix the code what you need to do is:

Allocate a buffer long enough to hold the final output. (Define a pointer and use allocated memory using malloc() or family, of sufficient size)
Use sprintf() to populate the memory with the output you need.
Return the pointer.
Once you're done using it, free() the returned pointer.

String variable assignment gives pointer error

2 Answers