How can I code the program to accept not only uppercase but also lowercase first letter?

For example, if I run the program and type in sin, it shows error. When I write down Sin, it’s ok. For example, if I run the program and type in sin, it shows error. When I write down Sin, it’s ok. For example, if I run the program and type in sin, it shows error. When I write down Sin, it’s ok. For example, if I run the program and type in sin, it shows error. When I write down Sin, it’s ok.

/*************************************************************
                            Pavel Kivilša
                               EKF-21
                        1 laboratorinis darbas
                               2021-11
*************************************************************/

#define _CRT_SECURE_NO_WARNINGS
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#include <math.h>

enum Functions { Floor, Round, Ceil, Sin, Cos, Cosh, Exp, Tan, Tanh, Sinh, Log, Log10, Sqrt, Pow, Trunc, Help };
enum Functions function_name;

int main(int argc, char* argv[]) {
    float number, number2;
    char* function[16] = { "Floor", "Round", "Ceil", "Sin", "Cos", "Cosh", "Exp", "Tan", "Tanh", "Sinh", "Log", "Log10", "Sqrt", "Pow", "Trunc", "Help" };

    char name[6];
    printf("Enter a math function: ");
    scanf("%s", name);

    for (function_name = 0; function_name <= 15; function_name++) {
        if (strcmp(function[function_name], name) == 0) {
            break;
        }
    }


    switch (function_name) {
    case Floor:
        printf("Enter the value of floor: ");
        scanf("%f", &number);
        printf("Floor of %.2f is equal to %.2f\n", number, floor(number));
        break;
    case Round:
        printf("Enter the value of round: ");
        scanf("%f", &number);
        printf("Round of %.2f is equal to %.2f\n", number, round(number));
        break;
    case Ceil:
        printf("Enter the value of ceil: ");
        scanf("%f", &number);
        printf("Ceil of %.2f is equal to %.2f\n", number, ceil(number));
        break;
    case Sin:
        printf("Enter the value of sin: ");
        scanf("%f", &number);
        printf("Sin of %.2f is equal to %.2f\n", number, sin(number));
        break;
    case Cos:
        printf("Enter the value of cos: ");
        scanf("%f", &number);
        printf("Cos of %.2f is equal to %.2f\n", number, cos(number));
        break;
    case Cosh:
        printf("Enter the value of cosh: ");
        scanf("%f", &number);
        printf("Cosh of %.2f is equal to %.2f\n", number, cosh(number));
        break;
    case Exp:
        printf("Enter the value of exp: ");
        scanf("%f", &number);
        printf("Exp of %.2f is equal to %.2f\n", number, exp(number));
        break;
    case Tan:
        printf("Enter the value of tan: ");
        scanf("%f", &number);
        printf("Tan of %.2f is equal to %.2f\n", number, tan(number));
        break;
    case Tanh:
        printf("Enter the value of tanh: ");
        scanf("%f", &number);
        printf("Tanh of %.2f is equal to %.2f\n", number, tanh(number));
        break;
    case Sinh:
        printf("Enter the value of sinh: ");
        scanf("%f", &number);
        printf("Sinh of %.2f is equal to %.2f\n", number, sinh(number));
        break;
    case Log:
        printf("Enter the value of log: ");
        scanf("%f", &number);
        printf("Log of %.2f is equal to %.2f\n", number, log(number));
        break;
    case Log10:
        printf("Enter the value of log10: ");
        scanf("%f", &number);
        printf("Log10 of %.2f is equal to %.2f\n", number, log10(number));
        break;
    case Sqrt:
        printf("Enter the value of sqrt: ");
        scanf("%f", &number);
        printf("Sqrt of %.2f is equal to %.2f\n", number, sqrt(number));
        break;
    case Pow:
        printf("Enter the value of pow: ");
        scanf("%f", &number);
        printf("Enter the second value of pow: ");
        scanf("%f", &number2);
        printf("%.2f to the power of %.2f is equal to %.2f\n", number, number2, pow(number, number2));
        break;
    case Trunc:
        printf("Enter the value of trunc: ");
        scanf("%f", &number);
        printf("Trunc of %.2f is equal to %.2f\n", number, trunc(number));
        break;
    case Help:
        printf("The following functions can be used: Floor, Round, Ceil, Sin, Cos, Cosh, Exp, Tan, Tanh, Sinh, Log, Log10, Sqrt, Pow, Trunc.\n");
        break;
    default:
        printf("Function not found, try again by typing in Help.\n");
        break;
    }
    return 0;
}

>Solution :

You are assigning to function_name

for (function_name = 0; function_name <= 15; function_name++) {

Which is not allowed in the C++ compiler you are using.

error C2440: '=': cannot convert from 'int' to 'Functions' note: Conversion to enumeration type requires an explicit cast (static_cast, C-style cast or function-style cast)

error C2676: binary '++': 'Functions' does not define this operator or a conversion to a type acceptable to the predefined operator

You could turn it into a C compiler by using the /TC switch and then the above will work.

If you wish to continue using C++, you need to cast. Here’s how you’d do it with C-style casts:

for (function_name = (Functions)0; function_name <= 15;
     function_name = (Functions)((int)function_name + 1))
{
    if (strcmp(function[function_name], name) == 0) {
        break;
    }
}

Using C++ style casts:

for (function_name = static_cast<Functions>(0); function_name <= 15; 
     function_name = static_cast<Functions>(static_cast<int>(function_name) + 1))
{
    if (strcmp(function[function_name], name) == 0) {
        break;
    }
}

Other notes:

You are missing #include <string.h> for strcmp and scanf("%s", &name); should be scanf("%s", name);