Split string according to space and convert each token to uppercase.

tokenize.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

char* strupper(char* s) {
    char* t = strdup(s);
    char* p = t;
    while( *p ) {
        *p = toupper(*p);
        p++;
    }
    return t;
}

int tokenize(char* s) {
    char *t = strdup(s);
    char *p = strtok(t, " ");
    printf("%s\n", strupper(p));
    while((p=strtok(NULL, " "))) {
        printf("%s\n", strupper(p));
    }
}

int main(int argc, char* argv[]) {
    tokenize("Hello world");
}