Hope that you can help meCode:#include <stdio.h> #include <string.h> #include <ctype.h> #define clean while(getchar() != '\n'); char s[36]; void cls(){ for(int i=0;i<50;i++)printf("\n"); } void header(){ cls(); printf("=================================================\n"); printf("Your current string : \"%s\"\n",s); printf("=================================================\n\n"); } void Input(void); void Reverse(void); void Upper(void); void CheckAl(void); int CheckWo(void); void Split(void); int main(){ int choose; cls(); do{ printf("Enter your first string [5..30] : "); scanf("%[^\n]s",&s);clean; }while(strlen(s) < 5 || strlen(s) > 30); do{ header(); printf("\nString Manipulator\n"); printf("====================\n"); printf("1. Input new string\n"); printf("2. Reverse the string\n"); printf("3. Uppercase the string\n"); printf("4. Check alphaber in the string\n"); printf("5. Checking word in the string\n"); printf("6. Split the string\n"); printf("7. Exit\n"); printf("Enter your choice : "); scanf("%d",&choose);clean; switch(choose){ case 1: Input(); break; case 2: Reverse(); break; case 3: Upper(); break; case 4: CheckAl(); break; case 5: CheckWo(); break; case 6: Split(); break; } }while(choose != 7); cls(); printf("Thank you, come again ^^");getchar(); return 0; } void Input(){ char s1[35]; header(); do{ printf("Enter the new string [5..30]: "); scanf("%[^\n]s",&s1);clean; }while(strlen(s1) < 5 || strlen(s1) > 30); strcpy(s,s1); } void Reverse(){ header(); printf("Reverse Successfully\n"); printf("Enter to continue.."); getchar(); strrev(s); } void Upper(){ header(); for(int i=0;i<strlen(s);i++){ s[i] = toupper(s[i]); } } void CheckAl(){ header(); printf("There are %d alphabet(s) in the string\n", strlen(s)); printf("Enter to continue.."); getchar(); } int CheckWo(){ header(); char s1[11]; do{ printf("What word do you want to search [3..10] ? "); scanf("%[^\n]s", &s1);clean; }while(strlen(s1) < 3 || strlen(s1) > 10); if(strstr(s,s1)){ printf("\"%s\" found..\n",s1); }else{ printf("\"%s\" not found..\n",s1); } printf("Enter to continue.."); getchar(); } ( The problem exist here ) void Split(){ header(); char s1[35]; strcpy(s1,s); const char sep[2] = " "; char *temp; temp = strtok(s1, sep); int i =1; while( temp != NULL ) { printf("Word %d : %s\n",i, temp ); temp = strtok(NULL, sep); i++; } printf("Enter to continue.."); getchar(); }