Un call n'est pas gratuit...
#include <stdio.h> void myToUpper(char* s) { while (s && *s) { if (*s >= 'a' && *s <= 'z') *s ^= 32; ++s; } } void myToLower(char* s) { while (s && *s) { if (*s >= 'A' && *s <= 'Z') *s ^= 32; ++s; } } int main(void) { char buff[] = "Un petit Test !"; printf("%s\n", buff); myToUpper(buff); printf("%s\n", buff); myToLower(buff); printf("%s\n", buff); return 0; }