CCS/MSP430G2553: Trying to find the time between max pulses so I can caluculate heart beats per minute

#include  "msp430g2253.h"
 
// Variables
int adc[50] = {0}; //Sets up an array of 10 integers and zero's the values
int avg_adc = 0;
 
// Function prototypes
void adc_Setup();
void adc_Sam10();
 
void main()
{
      WDTCTL = WDTPW + WDTHOLD;         // Stop WDT
      adc_Setup();                      // Fucntion call for adc_setup
 
      while(1)
      {
          long adctot = 0;
          adc_Sam10();      // Function call for adc_samp
          // Add all the sampled data and divide by 10 to find average
          int i = 0;
          for(i = 0; i <= 49; i++){
              adctot = adctot + adc[i];
          }
          avg_adc = adctot/50;
      }
}
 
// ADC10 interrupt service routine
#pragma vector=ADC10_VECTOR
__interrupt void ADC10_ISR(void)
{
  __bic_SR_register_on_exit(CPUOFF);        // Clear CPUOFF bit from 0(SR)
}
 
// ADC set-up function
void adc_Setup()
{
    ADC10CTL1 = CONSEQ_2 + INCH_0;                      // Repeat single channel, A0
    ADC10CTL0 = ADC10SHT_2 + MSC + ADC10ON + ADC10IE;   // Sample & Hold Time + ADC10 ON + Interrupt Enable
    ADC10DTC1 = 0x32;                                  // 1000 conversions
    ADC10AE0 |= 0x01;                                   // P1.0 ADC option select
}
 
// ADC sample conversion function
void adc_Sam10()
{
    ADC10CTL0 &= ~ENC;              // Disable Conversion
    while (ADC10CTL1 & BUSY);       // Wait if ADC10 busy
    ADC10SA = (int)adc;             // Transfers data to next array (DTC auto increments address)
    ADC10CTL0 |= ENC + ADC10SC;     // Enable Conversion and conversion start
    __bis_SR_register(CPUOFF + GIE);// Low Power Mode 0, ADC10_ISR
}