You might not have provided enough information for someone to help. But I'll take a stab. Also I think you have a typo and missed a comma in the code you did post.
I am assuming 'score' is an int and the function, TTF_RenderText_Solid is expecting a char* for the second arguement.
A simple way to do this would be:
char textBuffer[64];
sprintf(textBuffer, "%d", score); // Write the int 'score' into a char buffer
TTF_RenderText_Solid(font, textBuffer, textColor);
sprintf works just like printf but writes into a char buffer instead of standard out.
The error you received was pretty straight forward. You were trying to use a variable of type 'int' when a variable of type 'char*' was expected.