During Problem Set i came across the error Expected Expression on the statement
"string s = GetString();" Suggestions would be appreciated. The code is provided below.

    #include <cs50.h>
    #include <stdio.h>
    #include <string.h>
    #include <ctype.h>

    int main(void)
    {
        int s = 0; // Height
        int t = 0; // Line
        int u = 0; // Column

        do
        {
            // Gathers string.
            printf("Please provide the height of the pyramid: ");
            string s = GetString();
        }
        while (s < 1 || s > 23);

        // Selects a line.
        for (int t = 1; t <= s; t++)
        {
            // Selects a column.    
            for (int u = 1; u <= s; u++) 
            {
            // Prints character.
            if (u >= s + 1 - t)
            {
                printf("#");
            }
            else
            {
                printf(" ");
            }
            }
        }
        // Prints next line.
        printf("\n");
    }