Question

I am trying hands on one code in C where in I need to check whether the value being input by the user is integer or not. I tried isdigit() but it didn’t work. May I expect any help from you guys.

while(1) {

    printf( " \n -------------Enter your choice --------------------------\n ");
    printf("\n 1. Insertion \n 2. Preorder \n 3. Inorder \n 4. Postorder \n 5. Deletion \n 6. Search \n 7. Exit \n ");
    scanf ("%d", &save_the_input );

    switch(save_the_input) {

        case 1 : 
            printf( " \n......... Please enter the numbers to create the binary tree....... \n");
            scanf ("%d", &number_of_nodes);

            printf( "\n...... Please enter the numbers one by one... \n");

            for (iterator = 0; iterator < number_of_nodes; iterator++) {
                scanf ("%d", &user_input);
                if (( user_input < 0 )) {
                    printf( " ------- You have either entered a Character or a Negative number ----- \n ");
                    printf( " ------- Please enter the Positive integer values-------------\n ");
                    main();
                }
                else {
                    root_node = insert (root_node, user_input);
                    printf("\n");
                    printf("data element inserted is %d \n ", user_input);
                }
            }
            break;

Answer 1

You can use sscanf

int num;
ret = sscanf(line,"%d",&num);
if (ret == 1) {
    // num contains number
} else {
    // not a number
}