convertC

/*
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/*
 * File:   main.c
 * Author: NgT
 *
 * Created on July 15, 2016, 12:40 AM
 */

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

int value(char a) {
    if (a == '0') return 0;
    if (a == '1') return 1;
    if (a == '2') return 2;
    if (a == '3') return 3;
    if (a == '4') return 4;
    if (a == '5') return 5;
    if (a == '6') return 6;
    if (a == '7') return 7;
    if (a == '8') return 8;
    if (a == '9') return 9;
    if (a == 'A') return 10;
    if (a == 'B') return 11;
    if (a == 'C') return 12;
    if (a == 'D') return 13;
    if (a == 'E') return 14;
    if (a == 'F') return 15;
}

int checkBase(int n, char s[]) {
    int i;
    if (n == 2) {
        for (i = 0; i < strlen(s) - 1; i++) {
            if (s[i] == '1') continue;
            if (s[i] == '0') continue;
            return 1;
        }
    }
    if (n == 8) {
        for (i = 0; i < strlen(s) - 1; i++) {
            if (s[i] >= '0' && s[i] <= '7') continue;
            return 1;
        }
    }
    if (n == 16) {
        for (i = 0; i < strlen(s) - 1; i++) {
            if (s[i] >= '0' && s[i] <= '9') continue;
            if (s[i] >= 'A' && s[i] <= 'F') continue;
            return 1;
        }
    }
    return 0;
}

int convert(int n) {
    char s[100];
    do {
        printf("Enter base - %d: ", n);
        gets(s);
    } while (checkBase(n, s));
    int i, base = 1, dec = 0;
    for (i = strlen(s) - 1; i>-1; i--) {
        dec += value(s[i]) * base;
        base *= n;
    }
    return dec;
}

void read(int *n) {
    int a, k = 1;
    char c;

    do {
        if (k == 0) printf("Enter a number: ");
        k = scanf("%d%c", &a, &c);
        if (k == 0 || c != '\n') {
            k = 0;
            while (getchar() != '\n');
        }
    } while (k == 0);
    *n = a;
}

void solve() {
    int a;
    int result;
    printf("1. Bin to Dec\n");
    printf("2. Oct to Dec\n");
    printf("3. Hex to Dec\n");
    printf("4.  Exit\n");


    do {
        printf("Enter a number: ");
        read(&a);
        switch (a) {
            case 1: result = convert(2);
                printf("Result: %d\n", result);
                break;
            case 2: result = convert(8);
                printf("Result: %d\n", result);
                break;
            case 3: result = convert(16);
                printf("Result: %d\n", result);
                break;
        }
    } while (a != 4);
}
int main(int argc, char** argv) {

    solve();
    return (EXIT_SUCCESS);
}