gcd

#include<stdio.h>
int gcd(int a,int b)
{
	if(b==0){
		return a;
	}
	else{
		return gcd(b,a%b);
	}
}
int main()
{
	int a,b,c,n;
	scanf("%d%d%d",&a,&b,&c);
	n=gcd(a,b);
	n=gcd(n,c);
	printf("%d",n);
	return 0;
}

#include <stdio.h> int gcd(int a, int b) { while (b != 0) { int temp = b; b = a % b; a = temp; } return a; } int gcd3(int a, int b, int c) { return gcd(gcd(a, b), c); } int main() { int m, n, o; scanf("%d%d%d", &m, &n, &o); printf("%d\n", gcd3(m, n, o)); return 0; }

#include<stdio.h>
int main()
{
    int a,b,c,min,i;
    scanf("%d %d %d",&a,&b,&c);
    if(a<=b&&a<=c){
        min=a;
    }else if(b<=a&&b<=c){
        min=b;
    }else{
        min=c;
    }
    for(i=min;i>=1;i--){
        if(a%i==0&&b%i==0&&c%i==0){
            printf("%d",i);
            break;
        }
    }
   return 0;
}//将就看看吧

暴力算法（问就是懒得想其他算法）：

#include <stdio.h> 
int main() {
    int n,a,b,c;
    scanf("%d%d%d",&a,&b,&c);
    for(int i=1;;i++){
        if(a%i==0&&b%i==0&&c%i==0)
        n=i;
        if(i==a||i==b||i==c)
        break;
    }
    printf("%d",n);
    return 0;
}

辗转相除法

int main()
{
    int a,b,c;
    int i,m;
    scanf("%d %d %d",&a,&b,&c);
    while(i=a%b){
        a=b;
        b=i;
    }
    while(m=b%c){
        b=c;
        c=m;
    }
    printf("%d",c);    
    return 0;
}

递归法：
#include<stdio.h>
int main(){
    int b,i,j,n,m;
        scanf("%d %d %d",&i,&j,&n);
        while(i%j!=0)
        {
            b=i%j;
            i=j;
            j=b;
        }
        while(j%n!=0)
        {
            m=j%n;
            j=n;
            n=m;
        }
        printf("%d\n",n);
    return 0;
}

#include <stdio.h> int main() { int a,b,c,min; scanf("%d %d %d",&a,&b,&c); min=a; if (min>b){ min=b; }if (min>c){ min=c; } int gcd; for (int i=1;i<=min;i++){ if (a%i0&&b%i0&&c%i==0){ gcd=i; } } printf("%d",gcd); return 0; }