Question

I’m trying to make a simple code in c language (Stupid question, but I’m learning), I dont understand that this code gives me an error … I must be doing wrong, I can not know that I have to change…sorry for my English … thanks in advance to all

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

char* to_up(char* str_); 

int main()
{
    char any_phrase[] = "This is a phrase";
    printf("%s\n", to_up(any_phrase));
    printf("%s\n", to_up("this is another phrase"));
    return 0;
}

char* to_up(char* str_) 
{
    int i;
    for (i=0; str_[i]; i++) 
        str_[i] = toupper(str_[i]);
    return str_;
}

Answer 1

The reason for the error is that when you pass the string as “this is another phrase” on its own, as in not contained in a variable, the string is what’s known as a string literal. What this means, among other things, is that the string is constant: you simply are not allowed to modify.

To solve your problem you’d have to store the string in a variable so it is allowed to be modified by your to_up() function call since it modifies the contents of the string.